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2010 (with abstract)
	▼ Ordered by publication date

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105.    K. Inaba, and M. Yamashita

            "Time-of-Flight Imaging Method to Observe Signatures of Antiferromagnetically Ordered States of Fermionic Atoms in an Optical Lattice"

            Physical Review Letters 105 (17), 173002 (2010).

 

            ABSTRACT: We propose a simple method to detect the antiferromagnetic (AF) state of fermionic atoms in an optical lattice by combining a time-of-flight (TOF) imaging method and a Feshbach resonance. In this scheme, the nontrivial dynamics of fermionic atoms during the imaging process works as a probe with respect to the breaking of the translational symmetry in the AF state. Precise numerical simulations demonstrate that the characteristic oscillatory dynamics induced by the scattering process that transfers an AF ordering vector appears in TOF images, which can be easily observed experimentally.

 

104.    H. Kageshima

            "Study on Thermoelectric Properties of Graphene"

            Japanese Journal Of Applied Physics 49 (10), 100207 (2010).

 

            ABSTRACT: The thermoelectric properties of graphene are theoretically examined by using an experimentally derived conduction model and the Mott relation. The results indicate that reducing carrier scattering suppresses the thermoelectric power and enhances the thermoelectric figure of merit. These characteristics give hints as to how the graphene could be used as a material for thermoelectric conversion. (C) 2010 The Japan Society of Applied Physics

 

103.    Y. Komatsuzaki, K. Higashi, T. Kyougoku, K. Onomitsu, and Y. Horikoshi

            "Negative Differential Resistance in InGaAs/InAlAs Nanoscale In-Plane Structures"

            Japanese Journal Of Applied Physics 49 (10), 104001 (2010).

 

            ABSTRACT: Nanoscale in-plane structure devices are fabricated by electron beam lithography followed by electron cyclotron resonance reactive ion etching. We investigate the negative differential resistance (NDR) of InGaAs/InAlAs in-plane structure devices. The NDR appears in the current-voltage (I-V) characteristics of simple two-terminal in-plane short-channel devices. NDR characteristics depend on the effective channel width of in-plane gate transistors and become more pronounced when the channel conductance is increased by applying gate voltages. In a short-channel in-plane gate transistor, a more prominent NDR is observed and the NDR appears even at room temperature. In addition, the NDR onset voltage shifts to lower voltages when the channel length decreases. The NDR phenomenon is most likely caused by the real-space transfer of electrons from a high mobility channel to a low mobility layer. (C) 2010 The Japan Society of Applied Physics

 

102.    H. Nakano, K. Oguri, Y. Okano, and T. Nishikawa

            "Dynamics of femtosecond-laser-ablated liquid-aluminum nanoparticles probed by means of spatiotemporally resolved X-ray absorption spectroscopy"

            Applied Physics A-materials Science & Processing 101 (3)523-531 (2010).

 

            ABSTRACT: We investigated spatiotemporal evolution of expanding ablation plume of aluminum created by a 100-fs, 10(14)-10(15)-W/cm(2) laser pulse. For diagnosing dynamic behavior of ablation plume, we employed the spatiotemporally resolved X-ray absorption spectroscopy (XAS) system that consists of a femtosecond-laser-plasma soft X-ray source and a Kirkpatrick-Baez (K-B) microscope. We successfully assigned the ejected particles by analyzing structure of absorption spectra near the L (II,III) absorption edge of Al, and we clarified the spatial distribution of Al+ ions, Al atoms, and liquid droplets of Al in the plume. We found that the ejected particles strongly depend the irradiated laser intensity. The spatial distribution of atomic density and the expansion velocity of each type of particle were estimated from the spatiotemporal evolution of ablation particles. We also investigated a temperature of the aluminum fine particles in liquid phase during the plume expansion by analyzing the slope of the L (II,III) absorption edge in case of 10(14)-W/cm(2) laser irradiation where the nanoparticles are most efficiently produced. The result suggests that the ejected particles travel in a vacuum as a liquid phase with a temperature of about 2500 to 4200 K in the early stage of plume expansion.

 

101.    K. Kakuyanagi, S. Kagei, S. Saito, H. Nakano, and K. Semba

            "Generation of Non-Classical Microwave Photon States in an Inductor-Capacitor Resonator Coupled to a Superconducting Flux Qubit"

            Applied Physics Express 3 (10), 103101 (2010).

 

            ABSTRACT: The quantum nature of a sub-millimeter sized superconducting inductor-capacitor (LC) resonator is been demonstrated. By employing a series of pulse sequences that induce half a cycle of vacuum Rabi oscillations, we put a single microwave photons into an LC resonator from a superconducting flux qubit. Sub-Poissonian photon number distributions obtained by the Fourier transformation of observed quantum oscillations between the vertical bar n, e > and vertical bar n + 1, g > states (n: photon number in the resonator, g, e: qubit state) indicates the successful generation of non-classical photon states in an LC resonator. (C) 2010 The Japan Society of Applied Physics

 

100.    G. Q. Zhang, K. Tateno, H. Gotoh, and T. Sogawa

            "< 110 >-Oriented In0.04Ga0.96As Nanowires Laterally Grown on GaAs (311)B Substrate in Au-Catalyzed Vapor-Liquid-Solid Mode"

            Applied Physics Express 3 (10), 105002 (2010).

 

            ABSTRACT: We report on ternary InGaAs nanowires (NWs) with a < 110 > orientation laterally grown on a GaAs (311)B substrate in the Au-particle-catalyzed vapor-liquid-solid mode. We determined the structure and composition of the lateral NWs using transmission electron microscopy and X-ray energy-dispersive spectrometry measurements. With an In/Ga source mole ratio of 20 : 80, the composition of the lateral NW is In0.04Ga0.96As. We found that the addition of 4% indium changed the cross section of the lateral NW from the triangular shape of GaAs NWs to a trapezoidal shape. (C) 2010 The Japan Society of Applied Physics

 

99.    K. Yamazaki, and H. Yamaguchi

            "Resist Coating on Vertical Side Faces Using Conventional Spin Coating for Creating Three-Dimensional Nanostructures in Semiconductors"

            Applied Physics Express 3 (10), 106501 (2010).

 

            ABSTRACT: We have devised a new resist-coating method using spin coating for creating three-dimensional (3D) nanostructures in semiconductors. Using this method, we were able to successfully coat poly(methyl methacrylate) (PMMA) films on the vertical side faces of micrometer-order Si blocks. The use of a solvent with low viscosity was found to be effective for obtaining good uniformity in resist thickness. Moreover, Monte Carlo simulations of electron scattering revealed that fine patterning on both the opposite side faces of a Si block should be possible by simultaneous development followed by electron beam (EB) writing from opposite directions, despite electron scattering. (C) 2010 The Japan Society of Applied Physics

 

98.    K. Sumitomo, Y. Tamba, Y. Shinozaki, and K. Torimitsu

            "Confinement of Fluorescent Probes in Microwells on Si Substrates by Sealing with Lipid Bilayers"

            Applied Physics Express 3 (10), 107001 (2010).

 

            ABSTRACT: We investigated the optimum architecture for confining fluorescent probes in microwells on a Si substrate by covering it with a lipid bilayer. We modified the structure of the wells to prevent the lipid membrane from falling into them, and the overhang shape at the aperture improved the probability of confinement. The fluorescence intensity from the calcein confined in the wells remained unchanged for one hour or more, indicating that the probes remain stably in the wells without flowing out. An artificial cell sealed with the suspended membrane is a promising tool for the functional analysis of membrane proteins. (C) 2010 The Japan Society of Applied Physics

 

97.    X. B. Zhu, A. Kemp, S. Saito, and K. Semba

            "Coherent operation of a gap-tunable flux qubit"

            Applied Physics Letters 97 (10), 102503 (2010).

 

            ABSTRACT: We replace the Josephson junction defining a three-junction flux qubit's properties with a tunable direct current superconducting quantum interference devices (dc-SQUIDs) in order to tune the qubit gap during the experiment. We observe different gaps as a function of the external magnetic pre-biasing field and the local magnetic field through the dc-SQUID controlled by high-bandwidth on chip control lines. The persistent current and gap behavior correspond to numerical simulation results. We set the sensitivity of the gap on the control lines during the sample design stage. With a tuning range of several gigahertz on a qubit dynamics timescale, we observe coherent system dynamics at the degeneracy point. (C) 2010 American Institute of Physics. [doi:10.1063/1.3486472]

 

96.    T. Akasaka, Y. Kobayashi, and M. Kasu

            "Supersaturation in nucleus and spiral growth of GaN in metal organic vapor phase epitaxy"

            Applied Physics Letters 97 (14), 141902 (2010).

 

            ABSTRACT: Nucleus and spiral growth mechanisms of GaN were experimentally studied by varying the degree of supersaturation, sigma, in selective-area metal organic vapor phase epitaxy. The spiral growth rate of GaN increased proportionally to sigma(2) in the sigma range from 0.0632 to 0.230. The nucleus growth rate of GaN was much smaller than the spiral one in the sigma range. The nucleation rate was almost zero at sigma lower than 0.130, suddenly increased at higher sigma values, and reached similar to 10(7) cm(-2) s(-1) at sigma of 0.230. These results are consistent with a theoretical analysis [W. K. Burton, N. Cabrera, and F. C. Frank, Philos. Trans. R. Soc. London, Ser. A 243, 299 (1951)]. (C) 2010 American Institute of Physics. [doi:10.1063/1.3497017]

 

95.    D. Fukuoka, K. Oto, K. Muro, Y. Hirayama, and N. Kumada

            "Skyrmion Effect on the Relaxation of SpinWaves in a Quantum Hall Ferromagnet"

            Physical Review Letters 105 (12), 126802 (2010).

 

            ABSTRACT: Spin relaxation of two-dimensional electrons in a GaAs/AlGaAs quantum well was studied by time-resolved Kerr rotation measurements using a two-color pump and probe technique. In quantum Hall ferromagnets, the spin-wave relaxation is strongly influenced by the photogenerated Skyrmion and anti-Skyrmion pairs. By tuning the pump and probe lights to the lowest optical transition, an intrinsic filling factor dependence of spin relaxation is obtained without photogeneration of Skyrmions. The relaxation time of the spin wave presents a sharp peak at odd filling factors, accompanied by dips on both sides of it. The peculiar filling factor dependence of the spin-wave relaxation around quantum Hall ferromagnets can be explained by the interaction between the spin wave and Skyrmion. Observation of a similar feature around v = 1, 3, and 5 may suggest the existence of Skyrmions around higher odd filling factors.

 

94.    H. Takayanagi, R. Inoue, T. Akazaki, K. Tanaka, and I. Suemune

            "Superconducting transport in an LED with Nb electrodes"

            Physica C-superconductivity And Its Applications 470 (19)814-817 (2010).

 

            ABSTRACT: Superconducting transport is measured between two superconducting electrodes at the n-type semiconductor side of a superconductor-based LED where a Josephson junction is formed. The characteristics of the Josephson junction are found to be modulated by applying voltage to the normal electrode at the p-type semiconductor side. The Josephson junction characteristics show an extraordinary sensitivity to the radiative recombination process, which we estimate as the recombination efficiency. (C) 2010 Elsevier B.V. All rights reserved.

 

93.    H. Yamamoto, O. Matsumoto, A. Tsukada, and M. Naito

            "MBE growth and properties of T '-La2CuO4 thin films"

            Physica C-superconductivity And Its Applications 470 (20)1025-1028 (2010).

 

            ABSTRACT: We prepared thin films of T'-La2CuO4, which usually crystallizes in the T structure, by MBE, and investigated their properties while systematically changing the post-reduction conditions with a view towards obtaining superconductivity along the lines of the parent compound superconductors we have recently reported (O. Matsumoto et al., Phys. Rev. B 79 (2009) 100508(R)). The results indicate that the optimal reduction window is very narrow, near which metallic conductivity is obtained down to 50 K. The resistivity of the T'-La2CuO4 films is in the range of 10(-2)-10(-3)Omega cm, which is several orders of magnitude lower than that of the counterpart T-La2CuO4, the implication of which is briefly discussed from the viewpoint of the difference in electronic structure induced by different oxygen coordination. (C) 2010 Elsevier B.V. All rights reserved.

 

92.    O. Matsumoto, A. Tsukada, H. Yamamoto, T. Manabe, and M. Naito

            "Material characterization of superconducting T '-Nd2CuO4 films synthesized by metal organic decomposition"

            Physica C-superconductivity And Its Applications 470 (20)1029-1032 (2010).

 

            ABSTRACT: Recently we have achieved superconductivity in T'-RE2CuO4 (RE = Pr, Nd, Sm, Eu, and Gd), films by metal organic decomposition (MOD). In this article, we first report the cation off-stoichiometry effect, which aims at screening out the possibility of hole doping by cation deficiencies. We also investigated the structure and microstructure of superconducting T'-Nd2CuO4 films synthesized by MOD. This investigation aims at elucidating why MOD-grown Nd2CuO4 films become superconducting whereas our previous Nd2CuO4 films grown by molecular beam epitaxy were not superconducting. (C) 2010 Elsevier B.V. All rights reserved.

 

91.    T. Seki, H. Shibata, H. Takesue, Y. Tokura, and N. Imoto

            "Comparison of timing jitter between NbN superconducting single-photon detector and avalanche photodiode"

            Physica C-superconductivity And Its Applications 470 (20)1534-1537 (2010).

 

            ABSTRACT: We report the pulse-to-pulse timing jitter measurement of a niobium nitride (NbN) superconducting single-photon detector (SSPD) and a commercially available InGaAs avalanche photodiode (APD) at 1550 nm wavelength. A direct comparison of their timing jitter was performed using the same experimental configuration. The measured jitter of the SSPD and the APD are 75 and 84 Ps at full-width at half-maximum (FWHM), and 138 and 384 Ps at full-width at tenth-maximum (FWTM), respectively. Although the difference for the FWHM is small, the very small value of the FWTM of the SSPD indicates that the SSPD is more advantageous than the APD for various applications, such as fiber-based quantum key distribution (QKD). (C) 2010 Elsevier B.V. All rights reserved.

 

90.    A. Ishizawa, T. Nishikawa, A. Mizutori, H. Takara, S. Aozasa, A. Mori, H. Nakano, A. Takada, and M. Koga

            "Octave-spanning frequency comb generated by 250 fs pulse train emitted from 25 GHz externally phase-modulated laser diode for carrier-envelope-offset-locking"

            Electronics Letters 46 (19)1343-1344 (2010).

 

            ABSTRACT: Proposed is an approach to achieving a carrier-envelope-offset (CEO)-locked frequency comb with 25 GHz mode spacing in the telecommunications wavelength region. To achieve the approach, a 250 fs laser pulse train at a 25 GHz repetition rate was developed by intensity-and phase-modulating a seed light emitted from a continuous-wave laser diode and propagating it through a dispersive fibre. Using the authors' developed tellurite photonics crystal fibre with a high-nonlinear coefficient, octave-spanning supercontinuum generation in the 1.5 mu m band from a 250 MHz gated pulse train for CEO frequency detection was demonstrated.

 

89.    M. Notomi

            "Manipulating light with strongly modulated photonic crystals"

            Reports On Progress In Physics 73 (9), 096501 (2010).

 

            ABSTRACT: Recently, strongly modulated photonic crystals, fabricated by the state-of-the-art semiconductor nanofabrication process, have realized various novel optical properties. This paper describes the way in which they differ from other optical media, and clarifies what they can do. In particular, three important issues are considered: light confinement, frequency dispersion and spatial dispersion. First, I describe the latest status and impact of ultra-strong light confinement in a wavelength-cubic volume achieved in photonic crystals. Second, the extreme reduction in the speed of light is reported, which was achieved as a result of frequency dispersion management. Third, strange negative refraction in photonic crystals is introduced, which results from their unique spatial dispersion, and it is clarified how this leads to perfect imaging. The last two sections are devoted to applications of these novel properties. First, I report the fact that strong light confinement and huge light-matter interaction enhancement make strongly modulated photonic crystals promising for on-chip all-optical processing, and present several examples including all-optical switches/memories and optical logics. As a second application, it is shown that the strong light confinement and slow light in strongly modulated photonic crystals enable the adiabatic tuning of light, which leads to various novel ways of controlling light, such as adiabatic frequency conversion, efficient optomechanics systems, photon memories and photons pinning.

 

88.    S. Imagawa, K. Edagawa, K. Morita, T. Niino, Y. Kagawa, and M. Notomi

            "Photonic band-gap formation, light diffusion, and localization in photonic amorphous diamond structures"

            Physical Review B 82 (11), 115116 (2010).

 

            ABSTRACT: We report experimental and numerical studies on photonic band-gap (PBG) formation and light propagation in a recently proposed unique photonic structure, "photonic amorphous diamond (PAD)." PADs have been fabricated in a microwave regime, and the formation of a full three-dimensional (3D) PBG has been substantiated experimentally. This proves unambiguously that periodicity is not essential to the realization of a 3D-PBG, contrary to the common belief. The 3D-PBG has been demonstrated to be completely isotropic, regardless of the light polarization direction, which, in principle, cannot be realized in conventional photonic crystals. In passbands, the PAD has exhibited diffusive light propagation, where the scattering strength increases significantly as the frequency approaches the band edge, indicating a precursor of light localization. Localized states have indeed been identified at the band edges by a numerical calculation. Numerical studies have also indicated that the picture of dielectric and air bands in conventional photonic crystals can be applied to the PBG formation in PAD as well. These findings provide different insights into the physical origin of PBGs and issues such as light diffusion and localization in photonic materials.

 

87.    S. Matsuo, A. Shinya, T. Kakitsuka, K. Nozaki, T. Segawa, T. Sato, Y. Kawaguchi, and M. Notomi

            "High-speed ultracompact buried heterostructure photonic-crystal laser with 13 fJ of energy consumed per bit transmitted"

            Nature Photonics 4 (9)648-654 (2010).

 

            ABSTRACT: The ability to directly modulate a nanocavity laser with ultralow power consumption is essential for the realization of a CMOS-integrated, on-chip photonic network, as several thousand lasers must be integrated onto a single chip. Here, we show high-speed direct modulation (3-dB modulation bandwidth of 5.5 GHz) of an ultracompact InP/InGaAsP buried heterostructure photonic-crystal laser at room temperature by optical pumping. The required energy for transmitting one bit is estimated to be 13 fJ. We also achieve a threshold input power of 1.5 mu W, which is the lowest observed value for room-temperature continuous-wave operation of any type of laser. The maximum single-mode fibre output power of 0.44 mu W is the highest output power, to our knowledge, for photonic-crystal nanocavity lasers under room-temperature continuous-wave operation. Implementing a buried heterostructure leads to excellent device performance, reducing the active region temperature and effectively confining the carriers inside the cavity.

 

86.    H. Hibino, H. Kageshima, and M. Nagase

            "Epitaxial few-layer graphene: towards single crystal growth"

            Journal Of Physics D-applied Physics 43 (37), 374005 (2010).

 

            ABSTRACT: We review our research towards single-crystal growth of epitaxial few-layer graphene (FLG) on SiC substrates. We have established a method for evaluating the number of graphene layers microscopically using low-energy electron microscopy. Scanning probe microscopy in air is also useful for estimating the number-of-layers distribution in epitaxial FLG. The number-of-layers dependence of the work function and C1s binding energy is determined using photoelectron emission microscopy. We investigate the growth processes of epitaxial FLG on the basis of the microscopic observations of surface morphology and graphene distribution. To gain insights into the growth mechanism, we calculate the SiC surface structures with various C coverages using a first-principles scheme. Uniform bilayer graphene a few micrometres in size is obtained by annealing in UHV.

 

85.    K. Tamaki, and T. Tsurumaru

            "Security Proof of Quantum Key Distribution"

            Ieice Transactions On Fundamentals Of Electronics Communications And E93A (5)880-888 (2010).

 

            ABSTRACT: Quantum key distribution (QKD) is a way to securely expand the secret key to be used in One-time pad, and it is attracting great interest from not only theorists but also experimentalists or engineers who are aiming for the actual implementations. In this paper, we review the theoretical aspect of QKD, especially we focus on its security proof, and we briefly mention the possible problems and future directions.

 

84.    H. Takesue, T. Honjo, K. Harada, and B. Miquel

            "Quantum Communication Experiments Using Telecom-Band Entangled Photons"

            Ieice Transactions On Fundamentals Of Electronics Communications And E93A (5)903-909 (2010).

 

            ABSTRACT: Entanglement is expected to play a crucial role in the next-generation quantum communication systems. This paper reviews recent quantum communication experiments over optical fiber using 1.5-mu m telecom-band entangled photon pairs. After describing the telecom-band entanglement sources based on spontaneous parametric processes, we review three quantum communication experiments using entangled photons: a long-distance entanglement distribution, an entanglement-based quantum key distribution, and an entanglement swapping.

 

83.    H. Takesue, K. Harada, K. Tamaki, H. Fukuda, T. Tsuchizawa, T. Watanabe, K. Yamada, and S. Itabashi

            "Long-distance entanglement-based quantum key distribution experiment using practical detectors"

            Optics Express 18 (16)16777-16787 (2010).

 

            ABSTRACT: We report an entanglement-based quantum key distribution experiment that we performed over 100 km of optical fiber using a practical source and detectors. We used a silicon-based photon-pair source that generated high-purity time-bin entangled photons, and high-speed single photon detectors based on InGaAs/InP avalanche photodiodes with the sinusoidal gating technique. To calculate the secure key rate, we employed a security proof that validated the use of practical detectors. As a result, we confirmed the successful generation of sifted keys over 100 km of optical fiber with a key rate of 4.8 bit/s and an error rate of 9.1%, with which we can distill secure keys with a key rate of 0.15 bit/s. (C) 2010 Optical Society of America

 

82.    J. S. Yang, C. Nacci, K. Kanisawa, and S. Folsch

            "Atom-by-atom assembly and spectroscopy of In/InAs(111)A adatom chains by low-temperature scanning tunneling microscopy"

            Journal Of Vacuum Science & Technology B 28 (4)C5G1-C5G4 (2010).

 

            ABSTRACT: By means of low-temperature scanning tunneling microscopy at 5 K, the authors demonstrate the controlled and reversible vertical manipulation of native In adatoms on the InAs(111)A surface grown by molecular beam epitaxy. Monatomic In adatom chains are constructed by positioning In atoms one by one. Scanning tunneling spectroscopy and spatial mapping of the differential tunneling conductance reveal substantial along-chain electronic coupling. This coupling results in the formation of chain-localized quantum states, which can be described as the bonding ground-state orbital in an artificial linear molecule. (C) 2010 American Vacuum Society. [DOI:10.1116/1.3430546]

 

81.    T. Hatano, S. Amaha, T. Kubo, S. Teraoka, Y. Tokura, J. A. Gupta, D. G. Austing, and S. Tarucha

            "Transport properties of two laterally coupled vertical quantum dots in series with tunable interdot coupling"

            Applied Physics Letters 97 (6), 062108 (2010).

 

            ABSTRACT: We describe the electronic properties of a double dot for which the lateral coupling between the two vertical dots can be controlled in situ with a center gate voltage (V-c) and the current flows through the two dots in series. When V-c is large and positive, the two dots merge. As V-c is made less positive, two dots are formed whose coupling is reduced. We measure charging diagrams for positive and negative source-drain voltages in the weak coupling regime and observe current rectification due to the Pauli spin blockade when the hyperfine interaction between the electrons and the nuclei is suppressed. (C) 2010 American Institute of Physics. [doi:10.1063/1.3479525]

 

80.    E. Kuramochi, H. Taniyama, T. Tanabe, K. Kawasaki, Y. G. Roh, and M. Notomi

            "Ultrahigh-Q one-dimensional photonic crystal nanocavities with modulated mode-gap barriers on SiO2 claddings and on air claddings"

            Optics Express 18 (15)15859-15869 (2010).

 

            ABSTRACT: We report designs for a silicon-on-insulator (SOI) one-dimensional (1D) photonic crystal (PhC) nanocavity with modulated mode-gap barriers based on the lowest dielectric band. These cavities have an ultrahigh theoretical quality factor (Q) of 10(7)-10(8) while maintaining a very small modal volume of 0.6-2.0 (lambda/n)(3), which are the highest Q for any nanocavities with SiO2 under-cladding. We have fabricated these SOI 1D-PhC cavities and confirmed that they exhibited a Q of 3.6x10(5), which is also the highest measured Q for SOI-type PhC nanocavities. We have also applied the same design to 1D PhC cavities with air claddings, and found that they exhibit a theoretical quality factor higher than 10(9). The fabricated air-cladding 1D Si PhC cavities have showed a quality factor of 7.2x10(5), which is close to the highest Q value for 1D PhC cavities. (C) 2010 Optical Society of America

 

79.    T. Kubo, Y. Tokura, and S. Tarucha

            "Dephasing in an Aharonov-Bohm interferometer containing a lateral double quantum dot induced by coupling with a quantum dot charge sensor"

            Journal Of Physics A-mathematical And Theoretical 43 (35), 354020 (2010).

 

            ABSTRACT: We theoretically investigated the dephasing in an Aharonov-Bohm interferometer containing a lateral double quantum dot induced by coupling with a quantum dot charge sensor. We employed the interpolative second-order perturbation theory to include the charge sensing Coulomb interaction. It is shown that the visibility of the Aharonov-Bohm oscillation of the linear conductance decreases monotonically as the sensing Coulomb interaction increases. In particular, for a weak sensing interaction regime, the visibility decreases parabolically, and it behaves linearly for a strong sensing interaction regime.

 

78.    H. Takesue

            "Single-photon frequency down-conversion experiment"

            Physical Review A 82 (1), 013833 (2010).

 

            ABSTRACT: We report a single-photon frequency down-conversion experiment. Using the difference frequency generation process in a periodically poled lithium niobate waveguide, we successfully observed the phase-preserved frequency down-conversion of a coherent pulse train with an average photon number per pulse of <1, from the 0.7 mu m visible wavelength band to the 1.3 mu m telecom band. We expect this technology to become an important tool for flexible photonic quantum networking, including the realization of quantum repeater systems over optical fiber using atom-photon entanglement sources for the visible wavelength bands.

 

77.    H. Nakashima, K. Furukawa, Y. Kashimura, K. Sumitomo, Y. Shinozaki, and K. Torimitsu

            "Pattern Formation and Molecular Transport of Histidine-Tagged GFPs Using Supported Lipid Bilayers"

            Langmuir 26 (15)12716-12721 (2010).

 

            ABSTRACT: We fabricated a heterogeneous supported lipid bilayer (SLB) by employing binary lipid mixtures comprising a saturated acyl chain DSPC and an unsaturated acyl chain nickel-chelating lipid. By using the specific adsorption properties of histidine-tagged proteins (His-tagged GFPs) in relation to nickel-chelating lipids, we demonstrated protein pattern formation on the SLB corresponding to the phase separation pattern of the SLB. In addition, by using a lipid mixture consisting of an unsaturated acyl chain DOPC and a nickel-chelating lipid, and His-tagged GFPs, we succeeded in transporting the proteins along a hydrophilic micropattern on a SiO2 substrate. The protein transport is induced by the self-spreading behavior of a fluid SLB with a kinetic spreading coefficient beta = 10.4 mu m(2)s(-1). This method provides a guide for strategically carrying various biomolecules to specific positions by using a soft biointerface on a solid surface. In addition, the results demonstrate the importance of using techniques that allow the controlled manipulation of biomolecules based on the static or dynamic properties of the SLB platform.

 

76.    M. Tani, T. Koizumi, H. Sumikura, M. Yamaguchi, K. Yamamoto, and M. Hangyo

            "Time-Domain Coherent Anti-Stokes Raman Scattering Signal Detection for Terahertz Vibrational Spectroscopy Using Chirped Femtosecond Pulses"

            Applied Physics Express 3 (7), 072401 (2010).

 

            ABSTRACT: A new scheme for low-frequency coherent anti-Stokes Raman scattering spectroscopy (CARS) using chirped femtosecond pulses is proposed and demonstrated. Two chirped broadband optical pulses created terahertz (THz) polarization in the sample and generated CARS signal. The chirped CARS signal was then compressed by a pulse compressor and detected by a time gating technique. A resonant Raman band of GaSe at around 0.6 THz was successfully observed with the time-domain CARS technique. With the present system, CARS spectra from 0.2 to 5 THz are obtainable. (C) 2010 The Japan Society of Applied Physics

 

75.    S. Tanabe, Y. Sekine, H. Kageshima, M. Nagase, and H. Hibino

            "Half-Integer Quantum Hall Effect in Gate-Controlled Epitaxial Graphene Devices"

            Applied Physics Express 3 (7), 075102 (2010).

 

            ABSTRACT: High-quality monolayer graphene was grown on the Si face of SiC by thermal decomposition, and its electrical properties were investigated in top-gated devices. At 2 K, the carrier mobility of the graphene exceeded 10,000 cm(2) V-1 s(-1) and the half-integer quantum Hall effect was observed. The quantum Hall states were even observed at various carrier densities when top-gate bias was applied. These findings suggest high-quality epitaxial graphene possesses the unique nature of monolayer graphene and is robust against device fabrication, which holds potential for graphene-based electronics applications. (C) 2010 The Japan Society of Applied Physics

 

74.    T. Akasaka, Y. Kobayashi, and M. Kasu

            "Nucleus and Spiral Growth Mechanisms of GaN Studied by Using Selective-Area Metalorganic Vapor Phase Epitaxy"

            Applied Physics Express 3 (7), 075602 (2010).

 

            ABSTRACT: We used selective-area metalorganic vapor phase epitaxy to study Frank-van der Merwe growth mechanisms of GaN. Step-free GaN surfaces with the diameter of 15-50 mu m were fabricated within selective areas free of screw-type dislocations. The growth rate was independent of the area, indicating multi-nucleation growth. The nucleation rate was in a range of 10(5)-10(7) cm(-2) s(-1) and the average two-dimensional nucleus density was 5 x 10(6) cm(-2). Selective areas having screw-type dislocations resulted in double growth spirals consisting of monolayer steps. The degree of supersaturation near the growing surface calculated from the interstep distance was independent of the area. (C) 2010 The Japan Society of Applied Physics

 

73.    S. Miyamoto, K. Nishiguchi, Y. Ono, K. M. Itoh, and A. Fujiwara

            "Resonant escape over an oscillating barrier in a single-electron ratchet transfer"

            Physical Review B 82 (3), 033303 (2010).

 

            ABSTRACT: Single-electron escape from a metastable state over an oscillating barrier is experimentally investigated in silicon-based ratchet transfer. When the barrier is oscillating on a time-scale characteristic of the single-electron escape, synchronization occurs between the deterministic barrier modulation and the stochastic escape events. The average escape time as a function of its oscillation frequency exhibits a minimum providing a primary signature for resonant activation of single electrons.

 

72.    K. Hirama, Y. Taniyasu, and M. Kasu

            "Heterostructure growth of a single-crystal hexagonal AlN(0001) layer on cubic diamond (111) surface"

            Journal Of Applied Physics 108 (1), 013528 (2010).

 

            ABSTRACT: We demonstrate heterostructure growth of a hexagonal AlN(0001) layer on cubic diamond (111) surface and investigate the interface structure in order to achieve AlN/diamond heterojunction devices. From the initial growth, the single-crystal AlN(0001) layer grows on the diamond (111) surface with an in-plane epitaxial relationship [10 (1) over bar0](AlN)//[1 (1) over bar0](diamond). A high-resolution transmission electron microscope image shows an abrupt interface. Misfit dislocations are distributed periodically at the heterointerface due to the large lattice mismatch between AlN and diamond. Compared with the in-plane epitaxial relationship [11 (2) over bar0](AlN)//[1 (1) over bar0](diamond), [10 (1) over bar0](AlN)//[1 (1) over bar0](diamond) is energetically preferred because it has a higher bond density and, therefore, lower interfacial energy. (C) 2010 American Institute of Physics. [doi:10.1063/1.3452362]

 

71.    S. Suzuki, Y. Kobayashi, T. Mizuno, and H. Maki

            "Non-catalytic growth of graphene-like thin film near pattern edges fabricated on SiO2 substrates"

            Thin Solid Films 518 (18)5040-5043 (2010).

 

            ABSTRACT: Graphene-like thin films were grown on patterned SiO2 substrates by simple thermal chemical vapor deposition using ethanol. The film growth occurred preferentially in the vicinity of pattern edges. Catalytic metal is not necessary for the substrate or the pattern. The films consist of graphitic nanocrystals of several nanometer scale. In the electric properties, the field effect is observed at room temperature. (c) 2010 Elsevier B.V. All rights reserved.

 

70.    M. Zander, J. Herfort, K. Kumakura, H. P. Scohnherr, and A. Trampert

            "Epitaxial Heusler alloy Co2FeSi films on Si(111) substrates grown by molecular beam epitaxy"

            Journal Of Physics D-applied Physics 43 (30), 305004 (2010).

 

            ABSTRACT: The influence of growth temperature on the structural and magnetic properties of Heusler alloy Co2FeSi films grown on Si(1 1 1) substrates has been studied. Reflection high energy electron diffraction, double crystal x-ray diffraction (DCXRD) and transmission electron microscopy (TEM) measurements revealed that Co2FeSi layers were epitaxially grown on Si(1 1 1) substrates in an optimized growth temperature range 150 degrees C < T-G < 200 degrees C. From DCXRD measurements and TEM, it was shown that in the optimized temperature range the Co2FeSi/Si(1 1 1) films crystallize in the B2 + L2(1) structures. All layers are ferromagnetic and well-ordered films on Si(1 1 1) show high magnetic moments with an average value of (1140 +/- 250) emu cm(-3), which is in good agreement with the value of bulk Co2FeSi at 300 K. The magnetic anisotropy is correlated with the structural properties of the layers.

 

69.    J. D. Yang, M. R. Li, H. X. Li, Y. L. Yang, Y. Kashimura, C. Wang, K. Torimitsu, X. Q. Lu, and W. P. Hu

            "Characterization and Application of Self-Assembly Porphyrin with Four "Clips" on Gold Surface"

            Journal Of Physical Chemistry C 114 (28)12320-12324 (2010).

 

            ABSTRACT: Self-assembled monolayers (SAMs) of thiol-derivatized porphyrin molecules on Au substrate have attracted extensive interest for use in sensing, molecular recognition, and molecular electronics. Here, we synthesized tetra[p-(3-mercaptopropyloxy)phenyl]porphyrin (PPS4) with four "clips" for SAMs. The results demonstrated that PPS4 could form excellent SAMs on gold surface wherein the molecules oriented on substrates with a tilted angle. Self-assembled nanojunctions of PPS4 were fabricated by using gold nanogap electrodes (gap width: ca. 100 nm), which exhibited nonlinear current-voltage characteristics, indicating tunneling injection of current from Au electrodes into PPS4. With the light on/off, the nanojunctions switched between low/high impedance states as nanometer scaled photoswitchers.

 

68.    S. Suzuki, K. Yamaya, Y. Homma, and Y. Kobayashi

            "Activation energy of healing of low-energy irradiation-induced defects in single-wall carbon nanotubes"

            Carbon 48 (11)3211-3217 (2010).

 

            ABSTRACT: We analyzed defects created by low-energy irradiation in single-wall carbon nanotubes (SWCNTs) using Raman spectroscopy. The analysis is based on the recovery curves of the G/D ratio and there is no need to assume a specific functional form between the G/D ratio and the defect density. The obtained activation energies of defect healing are 0.7 or 1.4 eV, depending on the extent of the damage, which are close to the values for recombination barriers of vacancy-adatom defects. Calculated recovery curves of the G/D ratio at room temperature show that the recovery is so slow that almost no recovery is observed in a usual time scale, which is consistent with experimental results. (C) 2010 Elsevier Ltd. All rights reserved.

 

67.    M. Tabe, D. Moraru, M. Ligowski, M. Anwar, R. Jablonski, Y. Ono, and T. Mizuno

            "Single-Electron Transport through Single Dopants in a Dopant-Rich Environment"

            Physical Review Letters 105 (1), 016803 (2010).

 

            ABSTRACT: We show that single-electron transport through a single dopant can be achieved even in a random background of many dopants without any precise placement of individual dopants. First, we observe potential maps of a phosphorus-doped channel by low-temperature Kelvin probe force microscopy, and demonstrate potential changes due to single-electron trapping in single dopants. We then show that only one or a small number of dopants dominate the initial stage of source-drain current vs gate voltage characteristics in scaled-down, doped-channel, field-effect transistors.

 

66.    V. M. Kendon, K. Nemoto, and W. J. Munro

            "Quantum analogue computing"

            Philosophical Transactions Of The Royal Society A-mathematical Physical 368 (1924)3609-3620 (2010).

 

            ABSTRACT: We briefly review what a quantum computer is, what it promises to do for us and why it is so hard to build one. Among the first applications anticipated to bear fruit is the quantum simulation of quantum systems. While most quantum computation is an extension of classical digital computation, quantum simulation differs fundamentally in how the data are encoded in the quantum computer. To perform a quantum simulation, the Hilbert space of the system to be simulated is mapped directly onto the Hilbert space of the (logical) qubits in the quantum computer. This type of direct correspondence is how data are encoded in a classical analogue computer. There is no binary encoding, and increasing precision becomes exponentially costly: an extra bit of precision doubles the size of the computer. This has important consequences for both the precision and error-correction requirements of quantum simulation, and significant open questions remain about its practicality. It also means that the quantum version of analogue computers, continuous-variable quantum computers, becomes an equally efficient architecture for quantum simulation. Lessons from past use of classical analogue computers can help us to build better quantum simulators in future.

 

65.    K. Nozaki, T. Tanabe, A. Shinya, S. Matsuo, T. Sato, H. Taniyama, and M. Notomi

            "Sub-femtojoule all-optical switching using a photonic-crystal nanocavity"

            Nature Photonics 4 (7)477-483 (2010).

 

            ABSTRACT: Although high-speed all-optical switches are expected to replace their electrical counterparts in information processing, their relatively large size and power consumption have remained obstacles. We use a combination of an ultrasmall photonic-crystal nanocavity and strong carrier-induced nonlinearity in InGaAsP to successfully demonstrate low-energy switching within a few tens of picoseconds. Switching energies with a contrast of 3 and 10 dB of 0.42 and 0.66 fJ, respectively, have been obtained, which are over two orders of magnitude lower than those of previously reported alloptical switches. The ultrasmall cavity substantially enhances the nonlinearity as well as the recovery speed, and the switching efficiency is maximized by a combination of two-photon absorption and linear absorption in the InGaAsP nanocavities. These switches, with their chip-scale integratability, may lead to the possibility of low-power, high-density, all-optical processing in a chip.

 

64.    M. Rahlenbeck, M. Wagenknecht, A. Tsukada, D. Koelle, R. Kleiner, B. Keimer, and C. Ulrich

            "Raman light scattering study and microstructural analysis of epitaxial films of the electron-doped superconductor La-2 (-x) Ce (x) CuO4"

            European Physical Journal B 75 (4)461-467 (2010).

 

            ABSTRACT: We present a detailed temperature-dependent Raman light scattering study of optical phonons in molecular-beam-epitaxy-grown films of the electron-doped superconductor La-2 (-x) Ce (x) CuO4 close to optimal doping (x similar to 0.08, T (c) = 29 K and x similar to 0.1, T (c) = 27 K). The main focus of this work is a detailed characterization and microstructural analysis of the films. Based on micro-Raman spectroscopy in combination with X-ray diffraction, energy-dispersive X-ray analysis, and scanning electron microscopy, some of the observed phonon modes can be attributed to micron-sized inclusions of Cu2O. In the slightly underdoped film (x similar to 0.08), both the Cu2O modes and others that can be assigned to the La-2 (-x) Ce (x) CuO4 matrix show pronounced softening and narrowing upon cooling below T similar to T (c) . Based on control measurements on commercial Cu2O powders and on a comparison to prior Raman scattering studies of other high-temperature superconductors, we speculate that proximity effects at La-2 (-x) Ce (x) CuO4/Cu2O interfaces may be responsible for these anomalies. Experiments on the slightly overdoped La-2 (-x) Ce (x) CuO4 film (x similar to 0.1) did not reveal comparable phonon anomalies.

 

63.    Y. Kashimura, T. Goto, H. Nakashima, K. Furukawa, E. J. Wang, H. X. Li, W. P. Hu, and K. Torimitsu

            "Transistor Properties of Novel Organic Conducting Polymers Bearing Tetrathiafulvalene Units in the Backbone"

            Japanese Journal Of Applied Physics 49 (1), 01AB08 (2010).

 

            ABSTRACT: The organic field-effect transistor (OFET) properties of conducting polymers bearing a tetrathiafulvalene (TTF) unit in the backbone whose termini are capped with functional groups were investigated. The OFET devices were fabricated by a solution process under various fabrication conditions. All the devices showed typical p-type semiconducting behavior as expected from the electron-donating properties of TTF derivatives. Cast films exhibited higher field-effect mobilities than spin-coated films. Surface treatment with organic silane molecules produced no noticeable effects. When using thioacetyl-capped polymer, treatment of the OFET device in an ammonia atmosphere resulted in a field-effect mobility one order of magnitude higher than that of the pristine film. By contrast, there was no such enhancement with ethyl acetate-capped polymer. Atomic force microscopy observations revealed that the ammonia treatment promoted the ordering of the polymer chain, which resulted in improved electronic conduction. (C) 2010 The Japan Society of Applied Physics

 

62.    Q. Zhang, H. Takesue, C. Langrock, X. P. Xie, M. M. Fejer, and Y. Yamamoto

            "Hong-Ou-Mandel Dip Using Degenerate Photon Pairs from a Single Periodically Poled Lithium Niobate Waveguide with Integrated Mode Demultiplexer"

            Japanese Journal Of Applied Physics 49 (6), 064401 (2010).

 

            ABSTRACT: We experimentally observed a Hong-Ou-Mandle dip with photon pairs generated in a periodically poled reverse-proton-exchange lithium niobate waveguide with an integrated mode demultiplexer at a wavelength of 1.5 mu m. The visibility of the dip in the experiment was 80% without subtraction of any noise terms at a peak pump power of 4.4mW. The technology developed in the experiment can find various applications in the research field of linear optics quantum computation in fiber or quantum optical coherence tomography with near infrared photon pairs. (C) 2010 The Japan Society of Applied Physics

 

61.    H. Okamoto, T. Tawara, H. Gotoh, H. Kamada, and T. Sogawa

            "Growth and Characterization of Telecommunication-Wavelength Quantum Dots Using Bi as a Surfactant"

            Japanese Journal Of Applied Physics 49 (6), 06GJ01 (2010).

 

            ABSTRACT: Telecommunication-wavelength quantum dots (QDs) were successfully grown by metalorganic vapor phase epitaxy using a novel growth method in which trimethylbismuth (TMBi) was supplied during the growth. Supplying TMBi during the growth was confirmed to have a surfactant effect, but did not result in the formation of a bismuth-containing alloy. Using this growth method, the photoluminescence intensity and wavelength of the QDs were much improved. It was found that the QD size was increased during the growth of the InGaAs covering layer; this effect partly resembled activated alloy phase separation reported for molecular-beam-epitaxy-grown QDs. For the realization of high density and multilayer QDs, we confirmed that a much higher V/III ratio than that of usual growth conditions and a strain-compensation structure are effective, respectively. (C) 2010 The Japan Society of Applied Physics

 

60.    M. Kubovic, M. Kasu, H. Kageshima, and F. Maeda

            "Electronic and surface properties of H-terminated diamond surface affected by NO2 gas"

            Diamond And Related Materials 19 (7-9)889-893 (2010).

 

            ABSTRACT: Hydrogen-terminated diamond surface exhibits p-type conductivity during its exposure to air. To investigate this phenomenon, we examined the influence of different gases on the surface conductivity. Exposure to NO2 gas resulted in the biggest increase in conductivity, while H2O vapor decreased the surface conductivity. Moreover, even very low concentrations of NO2 molecules in air increased the hole sheet concentration, and with increasing NO2 concentration, the hole sheet concentration increased up to 2.3 x 10(14) cm(-2) (at 300 ppm NO2). This increase of hole sheet concentration was observed during exposure to NO2 gas and simultaneous adsorption of NO2 molecules on the diamond surface, while it decreased when the exposure stopped and NO2 molecules desorbed from the surface. X-ray photoelectron spectroscopy investigation showed upward band bending and partial oxidation of the hydrogen-terminated surface after exposure to air and NO2. FETs exposed to NO2 gas exhibited lower source and drain resistances, which led to a 1.8-fold increase of maximum drain current, transconductance increased 1.5-fold and maximum frequency of oscillation increased 1.6-fold. (C) 2010 Elsevier B.V. All rights reserved.

 

59.    N. Kasai, C. S. Ramanujan, I. Fujimoto, A. Shimada, J. F. Ryan, and K. Torimitsu

            "AFM observation of single, functioning ionotropic glutamate receptors reconstituted in lipid bilayers"

            Biochimica Et Biophysica Acta-general Subjects 1800 (7)655-661 (2010).

 

            ABSTRACT: Background: Ionotropic glutamate receptors (iGluRs) are responsible for extracellular signaling in the central nervous system. However, the relationship between the overall structure of the protein and its function has yet to be resolved. Atomic force microscopy (AFM) is an important technique that allows nano-scale imaging in liquid. In the present work we have succeeded in imaging by AFM of the external features of the most common iGluR, AMPA-R (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor), in a physiological environment. Methods: Homomeric GluR3 receptors were over-expressed in insect cells, purified and reconstituted into lipid membranes. AFM images were obtained in a buffer from membranes immobilized on a mica substrate. Results: Using Au nanoparticle-conjugated antibodies, we show that proteins reconstitute predominantly with the N-terminal domain uppermost on the membrane. A tetrameric receptor structure is clearly observed, but it displays considerable heterogeneity, and the dimensions differ considerably from cryo-electron microscopy measurements. Conclusions: Our results indicate that the extracellular domains of AMPA-R are highly flexible in a physiological environment. General significance: AFM allows us to observe the protein surface structure, suggesting the possibility of visualizing real time conformational changes of a functioning protein. This knowledge may be useful for neuroscience as well as in pharmaceutical applications. (C) 2010 Elsevier B.V. All rights reserved.

 

58.    M. J. Everitt, W. J. Munro, and T. P. Spiller

            "Quantum measurement with chaotic apparatus"

            Physics Letters A 374 (28)2809-2815 (2010).

 

            ABSTRACT: We study a dissipative quantum mechanical model of the projective measurement of a qubit. We demonstrate how a correspondence limit, damped quantum oscillator can realise chaotic-like or periodic trajectories that emerge in sympathy with the projection of the qubit state, providing a model of the measurement process. (C) 2010 Elsevier B.V. All rights reserved.

 

57.    T. Watanabe, K. Onomitsu, and H. Yamaguchi

            "Feedback Cooling of a Strained GaAs Micromechanical Beam Resonator"

            Applied Physics Express 3 (6), 065201 (2010).

 

            ABSTRACT: Active feedback cooling is an important technique for achieving the quantum ground state in micro/nanomechanical resonators. We studied the effect of tensile strain on the achievable minimum temperature and quantum occupation number by fabricating a doubly clamped beam resonator from a GaAs/InAlAs strained layer heterostructure. Despite the increase of the minimum temperature, we demonstrate that the occupation number can be decreased by applying tensile strain to the mechanical resonator. (C) 2010 The Japan Society of Applied Physics

 

56.    S. Takahashi, R. S. Deacon, K. Yoshida, A. Oiwa, K. Shibata, K. Hirakawa, Y. Tokura, and S. Tarucha

            "Large Anisotropy of the Spin-Orbit Interaction in a Single InAs Self-Assembled Quantum Dot"

            Physical Review Letters 104 (24), 246801 (2010).

 

            ABSTRACT: The anisotropy of the spin-orbit interaction (SOI) is studied for a single uncapped InAs self-assembled quantum dot holding just a few electrons. The SOI energy is evaluated from anticrossing or SOI-induced hybridization between the ground and excited states with opposite spins. The magnetic angular dependence of the SOI energy falls on an absolute cosine function for azimuthal rotation, and a cosinelike function for tilting rotation. Furthermore, the SOI energy is quenched for a specific magnetic field vector. The angular dependence of SOI is found to compare well with calculation of Rashba SOI in a two-dimensional harmonic potential.

 

55.    K. Inaba, and M. Yamashita

            "Thermodynamic properties of two-component fermionic atoms trapped in a two-dimensional optical lattice"

            Physical Review A 81 (6), 063615 (2010).

 

            ABSTRACT: We study the finite-temperature properties of two-component fermionic atoms trapped in a two-dimensional (2D) optical lattice. We apply the self-energy functional approach to the 2D Hubbard model with a harmonic-trapping potential, and systematically investigate the thermodynamic properties of this system. We find that entropy and grand potential provide evidence of a crossover between the Mott-insulating and the metallic phases at certain temperatures. In addition, we find that entropy exhibits a cusplike anomaly at lower temperatures, suggesting a second-or higher-order antiferromagnetic transition. We estimate the antiferromagnetic transition temperatures, and clarify how the trapping potential affects this magnetic transition.

 

54.    H. Deng, H. Haug, and Y. Yamamoto

            "Exciton-polariton Bose-Einstein condensation"

            Reviews Of Modern Physics 82 (2)1489-1537 (2010).

 

            ABSTRACT: In the past decade, a two-dimensional matter-light system called the microcavity exciton-polariton has emerged as a new promising candidate of Bose-Einstein condensation (BEC) in solids. Many pieces of important evidence of polariton BEC have been established recently in GaAs and CdTe microcavities at the liquid helium temperature, opening a door to rich many-body physics inaccessible in experiments before. Technological progress also made polariton BEC at room temperatures promising. In parallel with experimental progresses, theoretical frameworks and numerical simulations are developed, and our understanding of the system has greatly advanced. In this article, recent experiments and corresponding theoretical pictures based on the Gross-Pitaevskii equations and the Boltzmann kinetic simulations for a finite-size BEC of polaritons are reviewed.

 

53.    I. Mahboob, C. Froitier, and H. Yamaguchi

            "A symmetry-breaking electromechanical detector"

            Applied Physics Letters 96 (21), 213103 (2010).

 

            ABSTRACT: The dynamical double well potential underpinning the stable oscillation phases in an electromechanical parametric resonator is manipulated via a secondary field excitation applied at the natural frequency of the oscillator. This enables symmetry to be lifted in the dynamical potential well and results in the parametric resonator oscillating with a preferred phase. The ability to break symmetry in the dynamical double well potential permits the realization of a symmetry-breaking detector which can resolve resonance frequency (f(0)) shifts of delta f(0)/f(0)similar to 10(-7) in a single-shot measurement. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3429589]

 

52.    Y. Taniyasu, and M. Kasu

            "Surface 210 nm light emission from an AlN p-n junction light-emitting diode enhanced by A-plane growth orientation"

            Applied Physics Letters 96 (22), 221110 (2010).

 

            ABSTRACT: (11(2) over bar 0) A-plane AlN p-n junction light-emitting diode (LED) with a wavelength of 210 nm is demonstrated. The electroluminescence from the A-plane LED is inherently polarized for the electric field parallel to the [0001] c-axis due to a negative crystal-field splitting energy. The polarization ratio (electric-field component ratio of parallel and perpendicular to c-axis) is as high as 0.9. The radiation pattern of the A-plane LED shows higher emission intensity along the surface normal, while that of a conventional (0001) C-plane LED shows lower emission intensity along the surface normal. The different radiation patterns can be explained by the polarization property. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3446834]

 

51.    I. Suemune, Y. Hayashi, S. Kuramitsu, K. Tanaka, T. Akazaki, H. Sasakura, R. Inoue, H. Takayanagi, Y. Asano, E. Hanamura, S. Odashima, and H. Kumano

            "A Cooper-Pair Light-Emitting Diode: Temperature Dependence of Both Quantum Efficiency and Radiative Recombination Lifetime"

            Applied Physics Express 3 (5), 054001 (2010).

 

            ABSTRACT: A light-emitting diode (LED) in the optical-fiber communication band showed special features after replacing the n-type electrode with niobium (Nb) superconducting metal. Nb electrodes prepared on an InGaAs-based semiconductor surface formed a superconductor/semiconductor/superconductor junction, and the current-voltage characteristics exhibited both DC and AC Josephson junction properties. This was a result of the injection of electron Cooper-pairs into the n-InGaAs active layer of an LED. The drastic enhancement of the electroluminescence output observed below the Nb superconducting critical temperature, T-c, demonstrates the active role of electron Cooper-pairs in radiative recombination. Lifetime measurements of this LED and accurate evaluation of the luminescence output made it possible to estimate the radiative recombination lifetimes. A theoretical formula derived for the Cooper-pair radiative recombination accurately describes both the measured steep reduction of the radiative recombination lifetime and the observed enhancement of the internal quantum efficiency below Tc. This work will assist the development of interdisciplinary physics and new applications in superconductivity and optoelectronics. (C) 2010 The Japan Society of Applied Physics

 

50.    H. Kageshima, and A. Fujiwara

            "Dielectric constants of atomically thin silicon channels with double gate"

            Applied Physics Letters 96 (19), 193102 (2010).

 

            ABSTRACT: Dielectric constants of Si (111) nanofilms with the double gate are studied in the full inversion regime by using the first-principles calculation. The calculations show that the dielectric constants are significantly smaller than that of the bulk. Further, the dielectric constants depend on the conduction type as well as on the film thickness. They also oscillate with a 2-bilayer-thickness for the p-channel case as the film thickness decreases. The suppressed dielectric constants are found in the channel center as well as in the channel surface. These findings open the way to artificial control of the dielectric constant in semiconductor nanostructures. (C) 2010 American Institute of Physics. [doi:10.1063/1.3427364]

 

49.    K. Yamamoto, M. Adachi, T. Tawara, H. Gotoh, A. Nakamura, and J. Temmyo

            "Synthesis and characterization of ZnCdO/ZnO multiple quantum wells by remote-plasma-enhanced MOCVD"

            Journal Of Crystal Growth 312 (9)1496-1499 (2010).

 

            ABSTRACT: The synthesis and characterization of Zn0.85Cd0.15O/ZnO multiple quantum wells (MQWs) by remote-plasma-enhanced metalorganic chemical vapor deposition are reported. The X-ray diffraction satellite pattern is consistent with the existence of the periodicity of the MQWs. The quantum energy levels were investigated by observing the blue-shift of steady-state photoluminescence (PL) peak at low temperature. PL lifetime in MQWs measured by the time-resolved PL decreases from 70 to 54 ps with decreasing Zn0.85Cd0.15O well width, indicating the enhancement of the exciton recombination in the well layer. (C) 2010 Elsevier B.V. All rights reserved.

 

48.    K. Yamamoto, T. Tsuboi, T. Ohashi, T. Tawara, H. Gotoh, A. Nakamura, and J. Temmyo

            "Structural and optical properties of Zn(Mg,Cd)O alloy films grown by remote-plasma-enhanced MOCVD"

            Journal Of Crystal Growth 312 (10)1703-1708 (2010).

 

            ABSTRACT: We report the structural and optical properties of wurtzite-structure Zn(Mg,Cd)O ternary alloys. Wurtzite (0 0 0 1) Zn1-xCdxO and MgyZn1-yO films were grown on (11-20) sapphire substrates using remote-plasma-enhanced metalorganic chemical vapor deposition. The large bowing parameters of Zn1-xCdxO and MgyZn1-yO ternary alloys are 3.0 and 3.5, respectively, which reflects the large difference of each binary's electronegativity. We have analyzed the broadening of photoluminescence (PL) in Zn(Mg,Cd)O alloys on alloy content by taking into account the statistical alloy fluctuation and the localization of the exciton, and have clarified that the localization of the exciton strongly affects to PL full-width at half-maximum (FWHM) in Zn(Mg,Cd)O alloys. The alloy broadenings in steady-state PL of Zn(Mg,Cd)O alloys are in good agreement with the calculated tendency by the theoretical model based on the statistical alloy fluctuation, while PL FWHM of Zn1-xCdxO is three times larger than the calculated results. Moreover, as another way to confirm alloy broadening, we also have done time-resolved PL measurements and derived the localized depth of the exciton in ZnO-based system, indicating a good agreement with the tendency of PL FWHM broadening. (C) 2010 Elsevier B.V. All rights reserved.

 

47.    K. Ueda, and M. Kasu

            "High Temperature Operation of Boron-Implanted Diamond Field-Effect Transistors"

            Japanese Journal Of Applied Physics 49 (4), 04DF16 (2010).

 

            ABSTRACT: Diamond field effect transistors (FETs) with Pt or Al Schottky gate electrodes were fabricated on high-quality boron (B)-implanted layers formed by combining ion-implantation and high-pressure and high-temperature annealing. The high temperature characteristics of these FETs were examined. Pt-gate B-implanted diamond FETs showed maximum drain current (I-DS) of 0.16 mA/mm at gate voltage of -2 V and drain voltage of -20 V at 25 degrees C. The I-DS increased as temperature increased because of the activation of boron, and it showed maximum value of 3.9 mA/mm at similar to 200 degrees C. Al-gate FETs showed similar temperature dependence of I-DS, though the operation temperature and I-DS were higher than those of Pt-gate FETs. High-temperature operation of the B-implanted diamond FETs was possible above 550 degrees C without severe drain bulk leakage, though the maximum I-DS gradually decreased as temperature increased because of drain bulk leakage above 300 degrees C. (C) 2010 The Japan Society of Applied Physics

 

46.    K. Hirama, Y. Taniyasu, and M. Kasu

            "Hexagonal AlN(0001) Heteroepitaxial Growth on Cubic Diamond (001)"

            Japanese Journal Of Applied Physics 49 (4), 04DH01 (2010).

 

            ABSTRACT: Structural properties of a hexagonal aluminum nitride (AlN) (0001) layer grown on a cubic diamond (001) substrate by metalorganic vapor-phase epitaxy (MOVPE) are investigated to discuss its growth mechanism. It was found that the AlN layer consists of tilted and rotated domains, which are nucleated just on diamond (001) substrates at the initial growth stage. The tilted AlN domains form on the diamond {111} facets of the pits, which are created on the diamond (001) surface during the thermal cleaning in H-2. The AlN[0001] direction of the tilted domains is oriented normal to the diamond {111} facets because the atomic bonding configurations of AlN(0001) and diamond (111) planes are similar. On the other hand, two kinds of rotated AlN domains form on the diamond (001) surface. The [0001] direction of the rotated AlN domains is oriented normal to diamond (001) surface, and the AlN[10 (1) over bar0] or [11 (2) over bar0] direction is oriented to the diamond [1 (1) over bar0] direction. The formation of the two kinds of rotated AlN domains originates from the nucleation on two different diamond (001) terraces with one atomic layer height difference. (C) 2010 The Japan Society of Applied Physics

 

45.    F. Maeda, and H. Hibino

            "Thin Graphitic Structure Formation on Various Substrates by Gas-Source Molecular Beam Epitaxy Using Cracked Ethanol"

            Japanese Journal Of Applied Physics 49 (4), 04DH13 (2010).

 

            ABSTRACT: We have studied the growth of graphene by gas-source molecular beam epitaxy, with a cracked-ethanol source. Three substrates-Si substrate with thin oxide layer, c-surface of sapphire, and graphene layers formed on SiC-were used to draw out clues to the optimum conditions for graphene growth. Raman spectroscopy and X-ray photoelectron spectroscopy analyses indicate that hardly any or fairly small amounts of graphene are formed on the Si and sapphire, although thin films of graphitic material can be formed. We estimated nominal growth rates on the three substrates and found that the growth rate on the graphene was much smaller than those on the other two substrates. We studied the growth process of graphene on graphene by reflection high-energy electron diffraction and found that two-dimensional graphene islands grew laterally but their lateral orientations were not aligned. (C) 2010 The Japan Society of Applied Physics

 

44.    M. Yamaguchi, A. Shimada, K. Torimitsu, and N. Nakano

            "Multichannel Biosensing and Stimulation LSI Chip Using 0.18 mu m Complementary Metal-Oxide-Semiconductor Technology"

            Japanese Journal Of Applied Physics 49 (4), 04DL14 (2010).

 

            ABSTRACT: We designed 8-channel preamplifiers and multisite stimulation circuits on a 2.5 x 1.4 mm(2) chip using a 0.18 mu m complementary metal-oxide-semiconductor (CMOS) process for a microelectrode array measurement system. The size of a 1-channel preamplifier including a DC store/adder circuit is 930 x 120 mu m(2). An 8-channel programmable stimulator was integrated on the same die. The preamplifier circuits can amplify a small neural signal with a low noise and a low power consumption (2 mW/ch) using a chopper operation. The stimulation circuits can apply a voltage of +/-700 mV to any channel and with any timing using serial digital data control. The performance of the biphasic stimulation waveform generated by the designed LSI chip is the same as that generated with a conventional stimulation system. These functions were confirmed by connecting the LSI chip to a conventional measurement system. The system miniaturization achieved using the custom LSI chip will offer great advantages in terms of future brain machine interface applications. (C) 2010 The Japan Society of Applied Physics

 

43.    Y. Kashimura, K. Furukawa, and K. Torimitsu

            "Self-Spreading Supported Lipid Bilayer Passing through Single Nanogap Structure: Effect of Position of Dyes in Lipid Molecules"

            Japanese Journal Of Applied Physics 49 (4), 04DL15 (2010).

 

            ABSTRACT: We report the self-spreading behavior of single lipid bilayers containing 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) fluorophores on a patterned surface equipped with a single nanogap. We found that the behavior of the fluorophores around the nanogap depended on the position of the dyes in the lipid molecules. For acyl chain-labeled lipids, the fluorescence intensities decreased discontinuously before and after they passed through the nanogap, whereas little decrease was observed for a headgroup-labeled lipid. A possible mechanism can be explained in terms of the reorientation of dyes in a lipid bilayer. Acyl chain-labeled NBD fluorophores are known to loop back to a lipid-water interface in a lipid bilayer. Since this effect makes an effective size of the lipid molecule larger, dye molecules easily suffer from steric hindrance when they pass through a nanogap leading to the fluorescence intensity reduction. (C) 2010 The Japan Society of Applied Physics

 

42.    M. Nagase, H. Hibino, H. Kageshima, and H. Yamaguchi

            "Contact Conductance Measurement of Locally Suspended Graphene on SiC"

            Applied Physics Express 3 (4), 045101 (2010).

 

            ABSTRACT: The characteristics of suspended graphene membran structures formed by partial etching underneath SiC were revealed by using atomic force microscopy. The contact force dependence of topographic and electrical conductance images were measured with a metal (Rh) coated microprobe. The contact resistance value for locally suspended graphene was estimated to be about 80 mu Omega cm(2), which is 10000 times larger than that for surrounding graphene normally grown on SiC. The nonlinear current-voltage characteristics of the locally suspended graphene suggest tunneling junction formation between a metal nano-contact and suspended graphene. (C) 2010 The Japan Society of Applied Physics

 

41.    M. Hunault, H. Takesue, O. Tadanaga, Y. Nishida, and M. Asobe

            "Generation of time-bin entangled photon pairs by cascaded second-order nonlinearity in a single periodically poled LiNbO3 waveguide"

            Optics Letters 35 (8)1239-1241 (2010).

 

            ABSTRACT: Entangled photon pairs are one of the most important resources for the development of quantum communication technologies. In order to produce pulsed photon pairs in the telecommunication band from 1.5 mu m pump light, most of the previous experiments used two successive periodically poled lithium niobate (PPLN) waveguides. We report what we believe to be a new method using cascaded second-order nonlinearity in a single PPLN waveguide to produce high-purity time-bin entangled photon pairs. We confirmed the generation of entanglement through a two-photon interference experiment showing a coincidence fringe with a visibility of up to 97%. (C) 2010 Optical Society of America

 

40.    F. Maeda, and H. Hibino

            "Growth of few-layer graphene by gas-source molecular beam epitaxy using cracked ethanol"

            Physica Status Solidi B-basic Solid State Physics 247 (4)916-920 (2010).

 

            ABSTRACT: To obtain few-layer graphene (FLG), we propose a new growth process based on gas-source molecular beam epitaxy, in which a cracked-ethanol source is employed. To show the feasibility of this growth process, we tried to homoepitaxially grow FLG on epitaxial graphene formed on a SiC substrate. The results of Raman scattering, transmission electron microscopy, and in situ X-ray photoelectron spectroscopy analyses prove that graphene was formed on the substrate, indicating that our approach is feasible for the formation of wafer-scale FLG. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

 

39.    Y. S. Shin, T. Obata, M. Pioro-Ladriere, Y. Tokura, R. Brunner, T. Kubo, K. Yoshida, and S. Tarucha

            "Single electron spin addressing by using photon-assisted-tunneling in a double quantum dot including a micro-magnet"

            Physica E-low-dimensional Systems & Nanostructures 42 (4)825-829 (2010).

 

            ABSTRACT: In a numerical simulation we demonstrate spin readout by using photon assisted tunneling (PAT). We are using a realistic double quantum dot design including a micro-magnet. The micro-magnet generates different Zeeman fields between the two dots. If the photon frequency matches the energy difference of either the up-spin or the down-spin state between the two dots, the electron will be delocalized over the two dots by inter-dot PAT. We numerically simulate the micro-magnet induced stray field for various micro-magnet parameters and calculate the PAT spin readout performance. (C) 2009 Elsevier B.V. All rights reserved.

 

38.    T. Kubo, Y. Tokura, T. Hatano, S. Amaha, S. Teraoka, and S. Tarucha

            "Effects of observation on quantum interference in a laterally coupled double quantum dot using a quantum dot charge sensor"

            Physica E-low-dimensional Systems & Nanostructures 42 (4)852-855 (2010).

 

            ABSTRACT: We theoretically investigated the effects of the observation by a quantum dot charge sensor on an Aharonov-Bohm effect in a laterally coupled double quantum dot using the interpolative 2nd-order perturbation theory. In particular, we introduce the notion of the coherent indirect coupling, which characterizes the strength of the indirect coupling between two quantum dots via the reservoir. As the Coulomb interaction Vs for the charge sensing increases, the linear conductance through a double quantum dot decreases because of the many-body correlation effect. The visibility of Aharonov-Bohm oscillation in the linear conductance behaves super-linearly for weak sensing interaction regime and sub-linearly for strong sensing interaction regime. (C) 2009 Elsevier B.V. All rights reserved.

 

37.    H. Tamura, and S. Sasaki

            "Fano-Kondo effect in side-coupled double quantum dot"

            Physica E-low-dimensional Systems & Nanostructures 42 (4)864-867 (2010).

 

            ABSTRACT: We simulate the Kondo effect in an embedded quantum dot (QD) which is coupled to a side QD in the tight-binding model. The effect of the Coulomb interaction in the embedded QD is taken into account by the slave boson mean field theory. An analytic form of the conductance is derived by employing the scattering matrix formalism, and is expressed in terms of the Fano parameter and the broadening which are related to the tight-binding parameters. By analyzing the energy dependence of the conductance, we demonstrate that the Kondo effect is strongly modulated by the Fano effect as observed in a recent experiment. (C) 2009 Elsevier B.V. All rights reserved.

 

36.    S. Amaha, T. Hatano, H. Tamura, T. Kubo, S. Teraoka, Y. Tokura, D. G. Austing, and S. Tarucha

            "Charge states of a collinearly and laterally coupled vertical triple quantum dot device"

            Physica E-low-dimensional Systems & Nanostructures 42 (4)899-901 (2010).

 

            ABSTRACT: Three laterally laterally coupled vertical single quantum dots (tQDs) in a collinear arrangement, with common source and drain electrodes, are investigated. The tQDs are formed inside three connected pillars (mesal, mesa2, mesa3) with four side gate electrodes (Cl, G2 (G2'), G3). Three families of Coulomb oscillation lines corresponding to charges in the numbers of electrons in the three dots are observed, and the few-electron charge configurations can be assigned. We also discuss the separation of adjacent Coulomb peak lines in the stability diagram, indicating that the inter-dot Coulomb energy between adjacent dots (mesa1-mesa2 and mesa2-mesa3) is significantly larger than that between the two non-adjacent dots (mesa1-mesa3). (C) 2009 Elsevier B.V. All rights reserved.

 

35.    O. Klochan, A. P. Micolich, L. H. Ho, A. R. Hamilton, K. Muraki, and Y. Hirayama

            "Crystallographic anisotropy of the Zeeman splitting in 1D hole quantum wires"

            Physica E-low-dimensional Systems & Nanostructures 42 (4)967-970 (2010).

 

            ABSTRACT: In this work we study the Zeeman splitting in induced ballistic ID wires fabricated along two orthogonal crystallographic directions [(2) over bar 3 3] and [0 1 (1) over bar]. Our data shows that the g-factor anisotropy for the high symmetry [0 1 (1) over bar] direction can be explained by the ID confinement only, whereas in the case of [(2) over bar 3 3] direction, the interaction between the ID confinement and crystal anisotropy effects is evident. (C) 2009 Elsevier B.V. All rights reserved.

 

34.    S. Faniel, T. Matsuura, S. Mineshige, Y. Sekine, and T. Koga

            "Anisotropic spin interference in InGaAs/InAlAs rectangular loop arrays"

            Physica E-low-dimensional Systems & Nanostructures 42 (4)990-993 (2010).

 

            ABSTRACT: We report the experimental detection of the anisotropic spin-orbit interaction (SOI) in InGaAs/InAlAs quantum wells, using spin interference experiments in arrays of rectangular loops with their sides aligned to the [1 1 0] and [1 (1) over bar 0] crystallographic directions. While the gate voltage is tuned, the time reversal Aharonov-Casher (TRAC) oscillations exhibit higher frequencies when the loops have their longer side along the [1 1 0] direction, clearly highlighting the anisotropy of the SOL We find that a simple spin interferometer model, including both the Rashba and the Dresselhaus SOIs, reproduces qualitatively the TRAC oscillations. (C) 2009 Elsevier B.V. All rights reserved.

 

33.    Y. Tokura, T. Kubo, Y. S. Shin, K. Ono, and S. Tarucha

            "Quantum spin transport in magnetic-field-engineered nano-structures"

            Physica E-low-dimensional Systems & Nanostructures 42 (4)994-998 (2010).

 

            ABSTRACT: We theoretically investigated the resonant current that passes through a series coupled double quantum dots (QDs) subject to different Zeeman splittings under finite bias and strong Coulomb interaction conditions. When the Zeeman fields are different but collinear, there is always a single resonant peak. And when both Zeeman sub-levels of the QD near the source reservoir (probe QD) can be filled, we can expect the current to be strongly suppressed, which can be identified as a spin blockade. When the magnetic fields in each QD are non-collinear, we need to consider three parameters, the Zeeman energy in the probe (sample) dot, B-Zp(B-Zs) and the relative angle of these fields, 0. If the effect of the Coulomb interaction can be neglected, we can expect to observe four resonant peaks when B-Zp not equal B-Zs since the spin eigenstate in one QD has a finite tunnel matrix element with both spin eigenstates in the other QD. However, the Coulomb correlation modifies the result significantly. When B-Zp > B-Zs, we always found a single resonant peak as a function of the energy offset. The peak current is maximum when 0 = 0 and decreases monotonically for a larger 0 < pi/2. In contrast, when B-Zp < B-Zs, there were three peaks for 0 < pi/4 and two peaks for 0 > pi/4. (C) 2009 Elsevier B.V. All rights reserved.

 

32.    S. Watanabe, G. Igarashia, K. Hashimoto, N. Kumada, and Y. Hirayama

            "Spectroscopic study of nuclear magnetic resonance induced by oscillating electron spin domain walls"

            Physica E-low-dimensional Systems & Nanostructures 42 (4)999-1003 (2010).

 

            ABSTRACT: Nuclear electric resonance (NER), where nuclear spin resonance is mediated by oscillating electron-spin domain walls, is studied by applying radio-frequency electric fields to a GaAs-based two-dimensional electron system. In contrast with conventional resistively detected nuclear magnetic resonance, the NER signal appears not only at the resonance frequency, f(L), but also at f(L)/2.f(L)/3, and so on. The amplitudes of NER signal are semi-quantitatively explained using a simple model based on the spatial oscillation of a domain wall and the resultant spatial distribution of the spectral density of the fundamental and harmonic components. (C) 2009 Elsevier B.V. All rights reserved.

 

31.    M. Yamaguchi, S. Nomura, H. Tamura, and T. Akazaki

            "Photoluminescence spectra of gated undoped quantum well with lateral potential modulation in low electron density"

            Physica E-low-dimensional Systems & Nanostructures 42 (4)1167-1171 (2010).

 

            ABSTRACT: We measured the photoluminescence (PL) of a GaAs quantum well (QW) with a lateral potential modulation by the front-gate bias while changing both the electron density and electric field at low temperature. Near the onset of the two-dimensional electron gas, we observed an anomalous enhancement of PL intensity of the neutral exciton X-0 accompanied by a decrease in the intensity of the charged exciton X-. The sample was a 20-nm GaAs back-gate undoped QW with semi-transparent square-mesh surface gates. By comparing the results with those for a flat transparent surface gate sample we discuss the origin of this anomalous phenomenon. We present a possible explanation for this phenomenon, which is attributed to lateral drift motion of the X0 in a laterally modulated exciton potential. (c) 2009 Elsevier B.V. All rights reserved.

 

30.    S. M. Huang, Y. Tokura, H. Akimoto, K. Kono, J. J. Lin, S. Tarucha, and K. Ono

            "Spin Bottleneck in Resonant Tunneling through Double Quantum Dots with Different Zeeman Splittings"

            Physical Review Letters 104 (13), 136801 (2010).

 

            ABSTRACT: We investigated the electron transport property of the InGaAs/GaAs double quantum dots, the electron g factors of which are different from each other. We found that in a magnetic field, the resonant tunneling is suppressed even if one of the Zeeman sublevels is aligned. This is because the other misaligned Zeeman sublevels limit the total current. A finite broadening of the misaligned sublevel partially relieves this bottleneck effect, and the maximum current is reached when interdot detuning is half the Zeeman energy difference.

 

29.    Y. G. Roh, T. Tanabe, A. Shinya, H. Taniyama, E. Kuramochi, S. Matsuo, T. Sato, and M. Notomi

            "Strong optomechanical interaction in a bilayer photonic crystal"

            Physical Review B 81 (12), 121101 (2010).

 

            ABSTRACT: We fabricated bilayer photonic crystal (PhC) as large as 20x30 mu m possessing 200-nm-thick slabs and a 200-nm-thick air gap. Input power dependence of reflectance spectra indicates air gap reduction by 3.6 nm. Combining it with finite element method calculation we estimate optomechanically generated force per unit stored energy as 0.4 mu N/pJ, exhibiting strong optomechanical coupling. RF spectrum of reflected light reveals intensity modulation by thermal vibration of bilayer PhC, which also shows strong interaction of optical resonance mode and mechanical mode of bilayer PhC.

 

28.    Y. Utsumi, D. S. Golubev, M. Marthaler, K. Saito, T. Fujisawa, and G. Schon

            "Bidirectional single-electron counting and the fluctuation theorem"

            Physical Review B 81 (12), 125331 (2010).

 

            ABSTRACT: We investigate the direction-resolved full counting statistics of single-electron tunneling through a double quantum-dot system and compare with predictions of the fluctuation theorem (FT) for Markovian stochastic processes. Experimental data obtained for GaAs/GaAlAs heterostructures appear to violate the FT. After analyzing various potential sources for the discrepancy we conclude that the nonequilibrium shot noise of the quantum point contact electrometer, which is used to study the transport, induces strong dot-level fluctuations which significantly influence the tunneling statistics. Taking these modifications into account we find consistency with the FT.

 

27.    A. Yoko, and H. Namatsu

            "Nanoelectrode lithography using a flat mold with a pattern defined by different conductivities"

            Microelectronic Engineering 87 (5-8)931-935 (2010).

 

            ABSTRACT: Nanoelectrode lithography is a pattern duplication method that combines nanoimprint with an electrochemical reaction. The method can form an oxide pattern directly on a semiconductor or metal. This method can use flat molds with patterns defined by substances with different conductivities, while the conventional nanoimprint technique must use a mold with a relief pattern. In this paper, the mold pattern for the technique is defined with an oxide material on the surface of a conductive substrate. Nanoelectrode lithography itself can be used to form a flat mold by using a conductive mold with a relief pattern, which leaves an oxide pattern via the anodic oxidation of Si. AFM lithography also can utilize an electrochemical reaction in the air to generate an oxide pattern on a conductive substrate, which gives us a fiat mold. This paper shows that both types of flat mold can transfer a pattern to a target substrate. These strategies will allow us to realize on-demand mold fabrication, mold modification, and an easy way of obtaining a mold with a finer pattern. (C) 2009 Elsevier B.V. All rights reserved.

 

26.    J. Noborisaka, K. Nishiguchi, H. Kageshima, Y. Ono, and A. Fujiwara

            "Tunneling spectroscopy of electron subbands in thin silicon-on-insulator metal-oxide-semiconductor field-effect transistors"

            Applied Physics Letters 96 (11), 112102 (2010).

 

            ABSTRACT: We report the tunneling spectroscopy of thin silicon-on-insulator (SOI) metal-oxide-semiconductor field-effect transistors with tunneling gate oxide. When electrons are injected into a thin SOI well, the gate-tunneling current shows kink structures originating from quantized energy levels in the SOI well. From the theoretical consideration of the energy levels and their density of states, the observed features can be ascribed to electron tunneling into the in-plane fourfold degenerate valley subbands. Furthermore, inhomogeneous peak broadening of the kink structures in the experiment is well explained by the SOI thickness variation.

 

25.    H. Takesue, H. Fukuda, T. Tsuchizawa, T. Watanable, K. Yamada, Y. Tokura, and S. Itabashi

            "Entanglement generation using silicon wire waveguide"

            Optics And Spectroscopy 108 (2)160-164 (2010).

 

            ABSTRACT: We report the first entanglement generation experiments using silicon waveguide. Using highly efficient spontaneous four-wave mixing in a 1.09 cm long silicon nanowire waveguide at room temperature, we successfully generated high-purity time-bin and polarization entangled photon pairs in the 1.5 mu m band. We expect this entanglement source will solve the problems of previous telecom-band entanglement sources.

 

24.    T. Tanabe, H. Sumikura, H. Taniyama, A. Shinya, and M. Notomi

            "All-silicon sub-Gb/s telecom detector with low dark current and high quantum efficiency on chip"

            Applied Physics Letters 96 (10), 101103 (2010).

 

            ABSTRACT: We demonstrate channel selective 0.1-Gb/s photoreceiver operation at telecom wavelength using a silicon high-Q photonic crystal nanocavity with a laterally integrated p-i-n diode. Due to the good crystal property of silicon the measured dark current is only 15 pA. The linear and nonlinear characteristics are investigated in detail, in which we found that the photocurrent is enhanced of more than 10(5) due to the ultrahigh-Q (Q similar or equal to 10(5)). With the help of two-photon absorption, which is visible at a surprisingly low input power of 10(-8) W, the quantum efficiency of this device reaches similar to 10%. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3357427]

 

23.    G. Q. Zhang, K. Tateno, H. Gotoh, T. Sogawa, and H. Nakano

            "Structural, Compositional, and Optical Characterizations of Vertically Aligned AlAs/GaAs/GaP Heterostructure Nanowires Epitaxially Grown on Si Substrate"

            Japanese Journal Of Applied Physics 49 (1), 015001 (2010).

 

            ABSTRACT: We structurally, compositionally, and optically characterize vertically aligned AlAs/GaAs/GaP heterostructured nanowires (NWs) grown on a Si substrate used for the integration of an optically active material into Si-based technology and its band-gap engineering. The NWs were grown using Au colloidal nanoparticles as catalysts via the vapor-liquid-solid mode. By alternately changing the source material between Ga and Al, we grew GaAs/AlAs/GaAs/AlAs/GaAs NWs with a well-controlled periodic structure and composition on a GaP segment, which was epitaxially grown on a Si substrate. No dislocations induced by the lattice mismatch were found in the GaAs segment of the NWs grown on the GaP segment despite a lattice mismatch of as large as 4%. This is because the NWs have a particular columnar structure with nanoscale diameters and can therefore relax laterally and accommodate a high strain. Stacking faults exist in zinc-blende-structured GaP and GaAs segments, while the AlAs segment has a pure wurtzite crystal structure without any stacking faults. It is found that the stacking fault in III-V NWs is significantly dependent on the stacking fault energy and ionicity. With increasing ionicity, stacking faults can be more easily introduced, and these NWs tend to have a wurtzite crystal structure. In addition, owing to the high surface nonradiative recombination rate resulting from the surface states on the GaAs NW surface, the excitonic emission of photoluminescence from the bare GaAs NW segment has a decay time of as short as 30 ps. With the growth of an AlGaAs capping layer and GaAs outer shell layer, the decay time of the excitonic emission increased 46-fold, indicating an excellent passivation effect on the GaAs segment surface. (C) 2010 The Japan Society of Applied Physics

 

22.    V. Tonchev, B. Ranguelov, H. Omi, and A. Pimpinelli

            "Scaling and universality in models of step bunching: the "C+-C-" model"

            European Physical Journal B 73 (4)539-546 (2010).

 

            ABSTRACT: We recently introduced a novel model of step flow crystal growth - the so-called "C+-C-" model [B. Ranguelov et al., C.R. Acad. Bulgare Sci. 60, 389 (2007)]. In this paper we aim to develop a complete picture of the model's behaviour in the framework of the notion of universality classes. The basic assumption of the model is that the reference ("equilibrium") densities used to compute the supersaturation might be different on either side of a step, so C-L/C-R not equal 1 (L/R stands for left/right in a step train descending from left to right), and that this will eventually cause destabilization of the regular step train. Linear stability analysis considering perturbation of the whole step train shows that the vicinal is always unstable when the condition C-L /C-R > 1 is fulfilled. Numerical integration of the equations of step motion combined with an original monitoring scheme(s) results in obtaining the exact size- and time- scaling of the step bunches in the limit of long times (including the numerical prefactors). Over a broad range of parameters the surface morphology is characterized by the appearance of the minimal interstep distance at the beginning of the bunches (at the trailing edge of the bunch) and may be described by a single universality class, different from those already generated by continuum theories [A. Pimpinelli et al., Phys. Rev. Lett. 88, 206103 (2002), J. Krug et al., Phys. Rev. B 71, 045412 (2005)]. In particular, the scaling of the minimal interstep distance l(min) in the new universality class is shown to be l(min) = (S-n /N)(1/(n+1)), where N is the number of steps in the bunch, n is the exponent in the step-step repulsion law U similar to 1/d(0) (n) for two steps placed a distance d(0) apart and S-n is a combination of the model parameters. It is also shown that N scales with time with universal exponent 1/2 independent of n. For the regime of slow diffusion it is obtained for the first time that the time scaling depends only on the destabilization parameter C-L/C-R. The bunching outside the parameter region where the above scaling exists cannot be assigned to a specific universality class and thus should be considered non-universal.

 

21.    Y. Shinozaki, K. Sumitomo, K. Furukawa, H. Miyashita, Y. Tamba, N. Kasai, H. Nakashima, and K. Torimitsu

            "Visualization of Single Membrane Protein Structure in Stretched Lipid Bilayer Suspended over Nanowells"

            Applied Physics Express 3 (2), 027002 (2010).

 

            ABSTRACT: In this study, we observed the topology of a single protein in a stretched lipid bilayer (membrane) suspended over a nanoscale well using a fast-scanning atomic force microscope (AFM). The membrane was located stably enough on the well to prevent the leakage of a liquid placed in the well, and it allowed us to observe membrane stretching using an AFM. We successfully observed the gradual stretching of the suspended membrane. We also observed single bacteriorhodopsin proteins in the stretched membrane, and found that they maintained their trimeric structure, but that the distances between the trimers increased. (C) 2010 The Japan Society of Applied Physics

 

20.    D. Terasawa, S. Kozumi, A. Fukuda, M. Morino, K. Iwata, N. Kumada, Y. Hirayama, Z. F. Ezawa, and A. Sawada

            "Activation study of collective excitations of the soliton-lattice phase in the nu=1 double-layer quantum Hall state"

            Physical Review B 81 (7), 073303 (2010).

 

            ABSTRACT: We investigate thermal excitations of the pseudospin soliton lattice in the double-layer quantum Hall (QH) state at total Landau-level filling factor nu = 1 by detailed measurements of the activation energy gap, where the pseudospin represents the layer degree of freedom. In a tilted magnetic field, the activation energy gap of the double-layer nu = 1 QH state shows a minimum near the phase transition point between the commensurate and incommensurate states. From a comparison of the in-plane field dependence of the activation energy gap with theories, we suggest that the minimum in the activation energy gap is due to collective modes of the soliton lattice.

 

19.    O. Entin-Wohlman, A. Aharony, Y. Tokura, and Y. Avishai

            "Spin-polarized electric currents in quantum transport through tubular two-dimensional electron gases"

            Physical Review B 81 (7), 075439 (2010).

 

            ABSTRACT: Scattering theory is employed to derive a Landauer-type formula for the spin and the charge currents, through a finite region where spin-orbit interactions are effective. It is shown that the transmission matrix yields the spatial direction and the magnitude of the spin polarization. This formula is used to study the currents through a tubular two-dimensional electron gas. In this cylindrical geometry, which may be realized in experiment, the transverse conduction channels are not mixed (provided that the spin-orbit coupling is uniform). It is then found that for modest boundary scattering, each step in the quantized conductance is split into two, and the new steps have a nonzero spin conductance with the spin polarization perpendicular to the direction of the current.

 

18.    T. Obata, M. Pioro-Ladriere, Y. Tokura, Y. S. Shin, T. Kubo, K. Yoshida, T. Taniyama, and S. Tarucha

            "Coherent manipulation of individual electron spin in a double quantum dot integrated with a micromagnet"

            Physical Review B 81 (8), 085317 (2010).

 

            ABSTRACT: We report the coherent manipulation of electron spins in a double quantum dot integrated with a micromagnet. We performed electric dipole spin resonance experiments in the continuous wave (CW) and pump-and-pobe modes. We observed two resonant CW peaks and two Rabi oscillations of the quantum dot current by sweeping an external magnetic field at a fixed frequency. Two peaks and oscillations are measured at different resonant magnetic field, which reflects the fact that the local magnetic fields at each quantum dot are modulated by the stray field of a micromagnet. As predicted with a density matrix approach, the CW current is quadratic with respect to microwave (MW) voltage while the Rabi frequency (nu(Rabi)) is linear. The difference between the nu(Rabi) values of two Rabi oscillations directly reflects the MW electric field across the two dots. These results show that the spins on each dot can be manipulated coherently at will by tuning the micromagnet alignment and MW electric field.

 

17.    H. Kamata, T. Ota, K. Muraki, and T. Fujisawa

            "Voltage-controlled group velocity of edge magnetoplasmon in the quantum Hall regime"

            Physical Review B 81 (8), 085329 (2010).

 

            ABSTRACT: We investigate the group velocity of edge magnetoplasmons (EMPs) in the quantum Hall regime by means of time-of-flight measurement. The EMPs are injected from an Ohmic contact by applying a voltage pulse, and detected at a quantum point contact by applying another voltage pulse to its gate. We find that the group velocity of the EMPs traveling along the edge channel defined by a metallic gate electrode strongly depends on the voltage applied to the gate. The observed variation of the velocity can be understood to reflect the degree of screening caused by the metallic gate, which damps the in-plane electric field and, hence, reduces the velocity. The degree of screening can be controlled by changing the distance between the gate and the edge channel with the gate voltage.

 

16.    S. Miyatake, K. Inaba, and S. Suga

            "Three-component fermionic atoms with repulsive interaction in optical lattices"

            Physical Review A 81 (2), 021603 (2010).

 

            ABSTRACT: We investigate three-component (colors) repulsive fermionic atoms in optical lattices using the dynamical mean-field theory. Depending on the anisotropy of the repulsive interactions, either a color density-wave state or a color-selective staggered state appears at half filling. In the former state, pairs of atoms with two of the three colors and atoms with the third color occupy different sites alternately. In the latter state, atoms with two of the three colors occupy different sites alternately and atoms with the third color are itinerant throughout the system. When the interactions are isotropic, both states are degenerate. We discuss the results using an effective model.

 

15.    K. Tamaki, and G. Kato

            "Quantum circuit for the proof of the security of quantum key distribution without encryption of error syndrome and noisy processing"

            Physical Review A 81 (2), 022316 (2010).

 

            ABSTRACT: One of the simplest security proofs of quantum key distribution is based on the so-called complementarity scenario, which involves the complementarity control of an actual protocol and a virtual protocol [M. Koashi, e-print arXiv:0704.3661(2007)]. The existing virtual protocol has a limitation in classical postprocessing, i.e., the syndrome for the error-correction step has to be encrypted. In this paper, we remove this limitation by constructing a quantum circuit for the virtual protocol. Moreover, our circuit with a shield system gives an intuitive proof of why adding noise to the sifted key increases the bit error rate threshold in the general case in which one of the parties does not possess a qubit. Thus, our circuit bridges the simple proof and the use of wider classes of classical postprocessing.

 

14.    O. Klochan, J. C. Chen, A. P. Micolich, A. R. Hamilton, K. Muraki, and Y. Hirayama

            "Fabrication and characterization of an induced GaAs single hole transistor"

            Applied Physics Letters 96 (9), 092103 (2010).

 

            ABSTRACT: We have fabricated and characterized a single hole transistor in an undoped AlGaAs-GaAs heterostructure. Our device consists of a p-type quantum dot, populated using an electric field rather than modulation doping. Low temperature transport measurements reveal periodic conductance oscillations due to Coulomb blockade. We find that the low frequency charge noise is comparable to that in modulation-doped GaAs single electron transistors (SETs), and an order of magnitude better than in silicon SETs.

 

13.    R. Inoue, H. Takayanagi, T. Akazaki, K. Tanaka, and I. Suemune

            "Transport characteristics of a superconductor-based LED"

            Superconductor Science & Technology 23 (3), 034025 (2010).

 

            ABSTRACT: We investigated the transport characteristics between two superconducting electrodes at the n-type semiconductor side of a superconductor-based LED where a Josephson junction is formed. The characteristics of the Josephson junction are found to be modulated by applying voltage to the normal electrode at the p-type semiconductor side. The mechanism of the modulation can be categorized into three regimes, the gate control, the radiative recombination process and the nonequilibrium carrier injection, depending on the current injection from the p-side. Among these three regimes, the Josephson junction characteristics show an extraordinary sensitivity to the radiative recombination process, which we estimate as the recombination efficiency.

 

12.    A. Aharony, O. Entin-Wohlman, Y. Tokura, and S. Katsumoto

            "Spin filtering due to quantum interference in periodic mesoscopic networks"

            Physica E-low-dimensional Systems & Nanostructures 42 (3)629-633 (2010).

 

            ABSTRACT: We present several new results, extending our recent proposal of a spin filter based on a tight-binding model for a periodic chain of diamond-like loops [A. Aharony, O. Entin-Wohlman, Y. Tokura, S. Katsumoto, Phys. Rev. B 78 (2008) 125328]. In this filter, the Rashba spin-orbit interaction (which can be tuned by a perpendicular gate voltage) and the Aharonov-Bohm flux (due to a perpendicular magnetic field) combine to select only one propagating ballistic mode. For this mode, the electronic spins are fully polarized along a direction that can be controlled by the electric and magnetic fields and by the electron energy. All the other modes are evanescent. Generalizing the square diamonds into rhombi with arbitrary opening angles, we find that increasing these angles widens the parameter range for efficient filtering. A different gate voltage on the two sides of each rhombus is found to delocalize the electrons for energies on one side of the band center. We also compare our tight-binding model with models Which Use continuous quantum networks of one-dimensional wires, and find coincidence only when one chooses particular Site energies at the nodes of the network. (C) 2009 Elsevier B.V. All rights reserved.

 

11.    T. Tawara, H. Kamada, T. Tanabe, T. Sogawa, H. Okamoto, P. Yao, P. K. Pathak, and S. Hughes

            "Cavity-QED assisted attraction between a cavity mode and an exciton mode in a planar photonic-crystal cavity"

            Optics Express 18 (3)2719-2728 (2010).

 

            ABSTRACT: The photoluminescence spectra from a quantum-dot exciton weakly-coupled to a planar photonic-crystal cavity is experimentally investigated by temperature tuning. Significant resonance shifts of the cavity mode are observed as the cavity mode spectrally approaches that of the exciton mode, showing the appearance of cavity-to-exciton attraction or mode pulling. Cavity-mode spectral shifts are also found theoretically using a master equation model that includes incoherent pump processes for the coupled exciton and cavity, pure dephasing, and allows for photon emission via radiation modes and the leaky cavity mode. Both experiments and theory show clear cavity mode spectral shifts in the photoluminescence spectra, when certain coupling parameters are met. However, discrepancies between the experimental data and theory, including more pronounced spectral shifts in the measurements, indicate that other unknown mode-pulling effects may also be occurring. (C) 2010 Optical Society of America

 

10.    M. Jo, T. Kaizawa, M. Arita, A. Fujiwara, Y. Ono, H. Inokawa, J. B. Choi, and Y. Takahashi

            "Fabrication of double-dot single-electron transistor in silicon nanowire"

            Thin Solid Films 518S186-S189 (2010).

 

            ABSTRACT: We propose a simple method for fabricating Si single-electron transistors (SET) with coupled dots by means of a pattern-dependent-oxidation (PADOX) method. The PADOX method is known to convert a small one-dimensional Si wire formed on a silicon-on-insulator (SOI) substrate into a SET automatically. We fabricated a double-dot Si SET when we oxidized specially designed Si nanowires formed on SOI substrates. We analyzed the measured electrical characteristics by fitting the measurement and simulation results and confirmed the double-dot formation and the position of the two dots in the Si wire. (C) 2009 Elsevier B.V. All rights reserved.

 

9.    K. Harada, H. Takesue, H. Fukuda, T. Tsuchizawa, T. Watanabe, K. Yamada, Y. Tokura, and S. Itabashi

            "Frequency and Polarization Characteristics of Correlated Photon-Pair Generation Using a Silicon Wire Waveguide"

            Ieee Journal Of Selected Topics In Quantum Electronics 16 (1)325-331 (2010).

 

            ABSTRACT: We report the frequency and polarization characteristics of correlated photon pairs generated in a Si wire waveguide (SWW). We confirmed that the bandwidth for correlated photon-pair generation was at least >2.8 THz. Moreover, we carried out a classical four-wave mixing experiment using strong pump and idler lights to estimate the bandwidth for correlated photon-pair generation. The results indicated that it is possible to generate photon pairs over a bandwidth as large as similar to 12 THz. We also showed that the generation efficiencies of the signal and idler photons for the horizontal polarization mode were much higher than those for the vertical polarization mode. This is probably caused by the large efficiencies in the group indexes and the effective cross-sectional areas for the two polarization modes. Furthermore, the bandwidth for the correlated photon-pair generation in the vertical polarization mode was similar to +/- 1 THz, and this was much narrower than that for the horizontal polarization mode. The difference between the bandwidths of the two polarization modes indicates that the SWW dispersion for the vertical polarization mode is significantly larger than that for the horizontal polarization mode. We then confirmed that the noise photons generated by spontaneous Raman scattering in an SWW were suppressed to below the detection limit of our setup.

 

8.    Y. S. Shin, T. Obata, Y. Tokura, M. Pioro-Ladriere, R. Brunner, T. Kubo, K. Yoshida, and S. Tarucha

            "Single-Spin Readout in a Double Quantum Dot Including a Micromagnet"

            Physical Review Letters 104 (4), 046802 (2010).

 

            ABSTRACT: We use photon-assisted tunneling (PAT) and an inhomogeneous Zeeman field to demonstrate spin-selective PAT readout with a double quantum dot. The inhomogeneous Zeeman field is generated by a proximal micromagnet, which provides different stray fields between the two dots, resulting in an energy difference between the interdot PAT of the up-spin state and that of the down-spin state. We apply various external magnetic fields to modify the relative filling weight between the up-spin and down-spin states and detect it by using a charge detection technique to probe the PAT induced charge delocalization in the double dot.

 

7.    P. Giudici, K. Muraki, N. Kumada, and T. Fujisawa

            "Intrinsic Gap and Exciton Condensation in the v(T)=1 Bilayer System"

            Physical Review Letters 104 (5), 056802 (2010).

 

            ABSTRACT: We investigate the quasiparticle excitation of the bilayer quantum Hall (QH) system at a total filling factor v(T) = 1 in the limit of negligible interlayer tunneling under a tilted magnetic field. We show that the intrinsic quasiparticle excitation is of purely pseudospin origin and solely governed by the inter-and intralayer electron interactions. A model based on exciton formation successfully explains the quantitative behavior of the quasiparticle excitation gap, demonstrating the existence of a link between the excitonic QH state and the composite fermion liquid. Our results provide a new insight into the nature of the phase transition between the two states.

 

6.    G. Q. Zhang, K. Tateno, H. Gotoh, and H. Nakano

            "Parallel-aligned GaAs nanowires with < 110 > orientation laterally grown on [311]B substrates via the gold-catalyzed vapor-liquid-solid mode"

            Nanotechnology 21 (9), 095607 (2010).

 

            ABSTRACT: We report parallel aligned GaAs nanowires (NWs) with < 110 > orientation laterally grown on [311]B substrates via the vapor-liquid-solid mode and demonstrate their controllability and growth mechanism. We control the size, density, and site of the lateral NWs by using size-and density-selective Au colloidal particles and Au dot arrays defined by electron-beam lithography. The lateral NWs grow only along the [110] and [(1) over bar(1) over bar0] directions and formation of the stable facets of (111)B and (001) on the sides of the lateral NWs is crucial for lateral NW growth. We clarify the growth mechanism by comparing the growth results on [311]B, (311)A, and (001) substrates and the surface energy change of lateral and freestanding NWs.

 

5.    M. Kubovic, M. Kasu, and H. Kageshima

            "Sorption properties of NO2 gas and its strong influence on hole concentration of H-terminated diamond surfaces"

            Applied Physics Letters 96 (5), 052101 (2010).

 

            ABSTRACT: The hole concentration of hydrogen-terminated diamond surfaces was studied during exposure to different concentrations of NO2 gas. The hole concentration increased during adsorption of NO2 molecules on the diamond surface, and decreased when the exposure stopped and NO2 molecules desorbed from the surface. The increase in hole concentration can be directly linked to the NO2 concentration. The low NO2 concentration in air (similar to 20 ppb) is responsible the hole concentration normally measured in air, and with increasing NO2 concentration the maximum hole concentration increases even more. The time evolution of hole concentration was analyzed using the Elovich sorption model. Further analysis based on the Ritchie model indicated that an adsorbed NO2 molecule occupies two different surface sites. Temperature-dependent measurements indicate low activation energy between 0.1 and 0.2 eV.

 

4.    T. Kobayashi, S. Tsuruta, S. Sasaki, T. Fujisawa, Y. Tokura, and T. Akazaki

            "Kondo Effect in a Semiconductor Quantum Dot with a Spin-Accumulated Lead"

            Physical Review Letters 104 (3), 036804 (2010).

 

            ABSTRACT: We study the Kondo effect in a semiconductor quantum dot in contact with a spin-accumulated lead. The spin accmulation in a nonmagnetic semiconductor is realized by spin injection from a spin-polarized quantum point contact in combination with magnetic focusing, thus creating spin-unbalanced chemical potentials. We demonstrate that the spin splitting of the Kondo densities of states (DOS) for spin-up and spin-down electrons can be controlled by selectively shifting only the spin-up DOS using spin accumulation. We also show the possibility to recover the Kondo effect in a high magnetic field, by compensating for Zeeman splitting by spin accumulation.

 

3.    S. Tanaka, K. Morita, and H. Hibino

            "Anisotropic layer-by-layer growth of graphene on vicinal SiC(0001) surfaces"

            Physical Review B 81 (4), 041406 (2010).

 

            ABSTRACT: Epitaxial graphene is formed on vicinal SiC (0001) surfaces via high temperature annealing in vacuum. Steps act as a significant "kicker" of graphene nucleation to feed C atoms. At elevated temperatures, graphene growth is controlled by the decomposition of Si-C bonds at step edges, Si desorption, and C diffusion on the surface. The limited Si desorption is due to the dependence of the growth rate on the thickness of graphene layers. The fabricated graphene layer(s) acts as a Si-diffusion barrier, which in turn induces local thermal equilibrium between the graphene layer and the SiC surface. C atoms preferentially diffuse along the steps, resulting in anisotropic layer-by-layer growth, which is characteristic in this system.

 

2.    T. Ota, T. Hayashi, K. Muraki, and T. Fujisawa

            "Wide-band capacitance measurement on a semiconductor double quantum dot for studying tunneling dynamics"

            Applied Physics Letters 96 (3), 032104 (2010).

 

            ABSTRACT: We propose and demonstrate wide-band capacitance measurements on a semiconductor double quantum dot (DQD) to study tunneling dynamics. By applying phase-tunable high-frequency signals independently to the DQD and a nearby quantum-point-contact charge detector, we successfully measure current proportional to the capacitance associated with the single-electron motion over a wide frequency range from Hz to a few tens of GHz. Analyzing the phase and the frequency dependence of the signal allows us to extract the characteristic tunneling rates. We show that, by applying this technique to the interdot tunnel coupling regime, quantum capacitance reflecting the strength of the quantum-mechanical coupling can be measured.

 

1.    H. Takesue, and K. Shimizu

            "Effects of multiple pairs on visibility measurements of entangled photons generated by spontaneous parametric processes"

            Optics Communications 283 (2)276-287 (2010).

 

            ABSTRACT: Entangled photon-pair sources based on spontaneous parametric processes are widely used in photonic quantum information experiments. In this paper, we clarify the relationship between average photon-pair number and the visibility of two-photon interference (TPI) using those entanglement sources. We consider sources that generate distinguishable and indistinguishable entangled photon pairs, assuming coincidence measurements that use threshold detectors. We present formulas for the TPI visibility of a polarization entanglement that take account of all the high-order multi-pair emission events. Moreover, we show that the formulas can be approximated with simple functions of the average pair number when the photon collection efficiency is small. As a result, we reveal that an indistinguishable entangled pair provides better visibility than a distinguishable one. (C) 2009 Elsevier B.V. All rights reserved.