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2009 (with abstract)
	▼ Ordered by first author

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

            "Step-Free GaN Hexagons Grown by Selective-Area Metalorganic Vapor Phase Epitaxy"

            Applied Physics Express 2 (9), 091002 (2009).

 

            ABSTRACT: Selective-area metalorganic vapor phase epitaxy of GaN has been investigated using the optimized growth conditions for the layer (Frankvan der Merwe) growth and GaN-template substrates with low dislocation density. The surface of a GaN hexagon with 16-mu m diameter has a single wide terrace over almost the whole area (step-free surface), when there are no screw-type dislocations in the finite area. Step-free GaN hexagons grew in the two-dimensional nucleus growth mode and had approximately an eight times lower growth rate than that of a GaN film grown in the step-flow mode under the growth conditions used in this study. (C) 2009 The Japan Society of Applied Physics

 

2.    S. Amaha, T. Hatano, T. Kubo, S. Teraoka, Y. Tokura, S. Tarucha, and D. G. Austing

            "Stability diagrams of laterally coupled triple vertical quantum dots in triangular arrangement"

            Applied Physics Letters 94 (9), 092103 (2009).

 

            ABSTRACT: We investigate three vertical quantum dots (QDs) laterally coupled in a triangular arrangement forming a triple QD (tQD) with common source and drain electrodes. The three equidistant dot mesas each have one gate electrode allowing control of the electrochemical potential in each QD. From the stability diagrams observed by measuring current through the tQD on sweeping the voltages on two of the gate electrodes for different values of voltage on the third gate electrode, we build up part of the three-dimensional stability diagram. Our device can be useful to reveal the consequences of interdot coupling on electronic states in tQDs.

 

3.    S. Amaha, T. Kubo, T. Hatano, S. Teraoka, A. Shibatomi, Y. Tokura, and S. Tarucha

            "Rectifying Behavior in Laterally Coupled Self-Assembled Quantum Dots with Asymmetric Tunneling Barriers"

            Applied Physics Express 2 (1), 014501 (2009).

 

            ABSTRACT: We use laterally coupled two self-assembled quantum dots (QDs) to study the effect of asymmetric coupling to the source and drain electrodes. From the measured stability diagram, we confirm that one QD (Dot 1) is tunnel-coupled to the two electrodes, whereas the other (Dot 2) is only tunnel-coupled to one electrode. We observe the asymmetric current-voltage characteristics, when Dot 2 acts as an electron trap only for one bias polarity to impede the electron flow through Dot 1 due to the inter-dot Coulomb coupling. This phenomenon can be understood within the scheme of charge ratchet effect. (C) 2009 The Japan Society of Applied Physics

 

4.    H. L. Dong, H. X. Li, E. Wang, S. Yan, J. M. Zhang, C. M. Yang, I. Takahashi, H. Nakashima, K. Torimitsu, and W. P. Hu

            "Molecular Orientation and Field-effect Transistors of a Rigid Rod Conjugated Polymer Thin Films"

            Journal Of Physical Chemistry B 113 (13)4176-4180 (2009).

 

            ABSTRACT: Molecular orientation in thin films of a rigid rod conjugated polymer, a derivative of poly(para-phenylene ethynytene)s with linear side chains and thioacetyl end groups, was investigated by reflection-absorption infrared spectroscopy and X-ray diffraction technique. The results indicated that TA-PPE molecules tended to align with their backbone planes perpendicular to substrates, that is, with an "edge-on" molecular orientation in the films. Such molecular orientation is favorable for the efficient carrier transport in two-dimensional direction in the polymer films (i.e., via both the intrachain and interchain), so that high performance organic field-effect transistors were fabricated with hole mobility at around similar to 4.3 x 10(-3) cm(2)/VS.

 

5.    J. F. Dynes, H. Takesue, Z. L. Yuan, A. W. Sharpe, K. Harada, T. Honjo, H. Kamada, O. Tadanaga, Y. Nishida, M. Asobe, and A. J. Shields

            "Efficient entanglement distribution over 200 kilometers"

            Optics Express 17 (14)11440-11449 (2009).

 

            ABSTRACT: Here we report the first demonstration of entanglement distribution over a record distance of 200 km which is of sufficient fidelity to realize secure communication. In contrast to previous entanglement distribution schemes, we use detection elements based on practical avalanche photodiodes (APDs) operating in a self-differencing mode. These APDs are low-cost, compact and easy to operate requiring only electrical cooling to achieve high single photon detection efficiency. The self-differencing APDs in combination with a reliable parametric down-conversion source demonstrate that entanglement distribution over ultra-long distances has become both possible and practical. Consequently the outlook is extremely promising for real world entanglement-based communication between distantly separated parties. (C) 2009 Optical Society of America

 

6.    O. M. Fedorych, S. A. Studenikin, S. Moreau, M. Potemski, T. Saku, and Y. Hirayama

            "MICROWAVE MAGNETOPLASMON ABSORPTION BY A 2DEG STRIPE"

            International Journal Of Modern Physics B 23 (12-13)2698-2702 (2009).

 

            ABSTRACT: Microwave (MW) absorption by a high mobility 2DEG has been investigated experimentally using sensitive Electron Paramagnetic Resonance (EPR) cavity technique. It is found that MW absorption spectra are chiefly governed by confined magnetoplasmon excitations in a 2DEG stripe. Spectra of the 2D magnetoplasmons are studied as a function of magnetic field, MW frequency and carrier density. The electron concentration is tuned by illumination and monitored using optical photoluminescence technique.

 

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

            "Atom-By-Atom Quantum State Control in Adatom Chains on a Semiconductor"

            Physical Review Letters 103 (9), 096104 (2009).

 

            ABSTRACT: The vertical manipulation of native adatoms on a III-V semiconductor surface was achieved in a scanning tunneling microscope at 5 K. Reversible repositioning of individual In atoms on InAs(111)A allows us to construct one-atom-wide In chains. Tunneling spectroscopy reveals that these chains host quantum states deriving from an adatom-induced electronic state and substantial substrate-mediated coupling. Our results show that the combined approach of atom manipulation and local spectroscopy is capable to explore atomic-scale quantum structures on semiconductor platform.

 

8.    D. Fukuoka, N. Tanaka, K. Oto, K. Muro, Y. Hirayama, N. Kumada, and H. Yamaguchi

            "OPTICALLY INDUCED DYNAMIC NUCLEAR SPIN POLARIZATION IN QUANTUM HALL REGIME OBSERVED BY A TIME-RESOLVED KERR ROTATION"

            International Journal Of Modern Physics B 23 (12-13)2755-2759 (2009).

 

            ABSTRACT: The dynamics between electron and nuclear spins in quantum Hall regime is investigated by a time-resolved Kerr rotation (TRKR) spectroscopy carried down in tilted-field geometry. The spin-flip energy varies almost linearly with the applied magnetic field under the nuclear spin depolarizing radio frequency field and the helicity modulation of circularly polarized pump, while the spin-flip energy obtained under a circularly polarized pump deviates from linearly behavior. This deviation is ascribed to the Overhauser shift due to dynamic nuclear spin polarization (DNP). The DNP depends markedly on the filling factor and present peaks at even filling factors. These results can be well explained by a simple model based on the detailed balance between electron and nuclear spins.

 

9.    C. H. Fung, K. Tamaki, B. Qi, H. K. Lo, and X. F. Ma

            "SECURITY PROOF OF QUANTUM KEY DISTRIBUTION WITH DETECTION EFFICIENCY MISMATCH"

            Quantum Information & Computation 9 (1-2)131-165 (2009).

 

            ABSTRACT: In theory, quantum key distribution (QKD) offers unconditional security based on the laws of physics. However, as demonstrated in recent quantum hacking theory and experimental papers, detection efficiency loophole can be fatal to the security of practical QKD systems. Here, we describe the physical origin of detection efficiency mismatch in various domains including spatial, spectral, and time domains and in various experimental set-ups. More importantly, we prove the unconditional security of QKD even with detection efficiency mismatch. We explicitly show how the key generation rate is characterized by the maximal detection efficiency ratio between the two detectors. Furthermore, we prove that by randomly switching the bit assignments of the detectors, the effect of detection efficiency mismatch can be completely eliminated.

 

10.    Y. Furukawa, N. Kasai, and K. Torimitsu

            "Effect of Mg2+ on neural activity of rat cortical and hippocampal neurons in vitro"

            Magnesium Research 22 (3)174S-181S (2009).

 

            ABSTRACT: Mg2+ plays an important role in biological functions, similar to that of Ca2+. In terms of neural activity, it is well known that Mg2+ blocks the NMDA receptor. However, the relationship between Mg2+ and neural function has not been well understood. We have investigated the effect of low extracellular Mg2+ concentration ([Mg2+](o)) on neural activity in rat cortical and hippocampal neurons by using microelectrode array (MEA) measurements and glutamate measurements, with an enzyme modified MEA-based multi-array sensor. In this study, we investigated the effects of low [Mg2+](o) on intracellular Ca2+ concentration ([Ca2+](i)) using a confocal laser microscope and a flow cytometer with a fluorescence probe. The results indicate that low [Mg2+](o) has an effect on neural activity. The responses of cortical and hippocampal neurons to low [Mg2+](o) differed in the developmental period. The results suggest that hippocampal neurons are more sensitive to [Mg2+](o) than cortical neurons. The glutamate receptor distributions in the cortex and hippocampus may be different. Further investigation is required to understand the mechanisms of the Mg2+ effect on neural activity.

 

11.    T. Goto, H. Inokawa, and K. Torimitsu

            "Geometrical effect in submicrometer channel organic field effect transistors"

            Thin Solid Films 518 (2)579-582 (2009).

 

            ABSTRACT: The electrical behaviors of submicrometer bottom-gate bottom-contact organic field effect transistors (OFETs) with submicrometer channel lengths and channel widths were investigated. Short-channel effects (SCEs) were observed for devices with shorter channel lengths and wider channel widths. The SCEs were effectively suppressed by reducing the channel width to 50 nm. The relationship between the drain current density and the drain voltage normalized by their respective channel lengths revealed that the drain current characteristics of shorter length channels fall into two types: parasitic contact resistances at lower drain voltage and SCEs caused by the space charge limiting current at higher drain voltages. The carrier mobility was also investigated, and found to be enhanced in the narrower channel width. (C) 2009 Elsevier B.V. All rights reserved.

 

12.    L. D. Haret, T. Tanabe, E. Kuramochi, and M. Notomi

            "Extremely low power optical bistability in silicon demonstrated using 1D photonic crystal nanocavity"

            Optics Express 17 (23)21108-21117 (2009).

 

            ABSTRACT: We demonstrate optical bistability in silicon using a high-Q (Q > 10(5))one-dimensional photonic crystal nanocavity at an extremely low 1.6 mu W input power that is one tenth the previously reported value. Owing to the device's unique geometrical structure, light and heat efficiently confine in a very small region, enabling strong thermo-optic confinement. We also showed with numerical analyses that this device can operate at a speed of similar to 0.5 mu s. (C) 2009 Optical Society of America

 

13.    H. Hibino, S. Mizuno, H. Kageshima, M. Nagase, and H. Yamaguchi

            "Stacking domains of epitaxial few-layer graphene on SiC(0001)"

            Physical Review B 80 (8), 085406 (2009).

 

            ABSTRACT: We used low-energy electron microscopy (LEEM) and scanning tunneling microscopy (STM) to investigate domain structures of epitaxial few-layer graphene grown on SiC(0001). Dark-field (DF) LEEM images formed using (10) and (01) beams clearly indicate that bilayer graphene consists of two types of domains, which have threefold symmetry and are rotated by 180 degrees with respect to each other. The DF LEEM images show clear domain contrasts at energies where (10)- and (01)-beam intensities calculated for bulk graphite are largely different. This means that the two types of domains are different in stacking: AB and AC stackings. The stacking domains are also supported by the STM images of bilayer graphene showing both hexagonal and honeycomb patterns.

 

14.    H. Hibino, H. Kageshima, M. Kotsugi, F. Maeda, F. Z. Guo, and Y. Watanabe

            "Dependence of electronic properties of epitaxial few-layer graphene on the number of layers investigated by photoelectron emission microscopy"

            Physical Review B 79 (12), 125437 (2009).

 

            ABSTRACT: We used spectroscopic photoemission and low-energy electron microscopy to investigate the electronic properties of epitaxial few-layer graphene grown on 6H-SiC(0001). Photoelectron emission microscopy (PEEM) images using secondary electrons (SEs) and C 1s photoelectrons can discriminate areas with different numbers of graphene layers. The SE emission spectra indicate that the work function increases with the number of graphene layers and that unoccupied states in the few-layer graphene promote SE emission. The C 1s PEEM images indicate that the C 1s core level shifts to lower binding energies as the number of graphene layers increases, which is consistent with the reported thickness dependence of the Dirac point energy.

 

15.    Y. Hirayama, G. Yusa, K. Hashimoto, N. Kumada, T. Ota, and K. Muraki

            "Electron-spin/nuclear-spin interactions and NMR in semiconductors"

            Semiconductor Science And Technology 24 (2), 023001 (2009).

 

            ABSTRACT: The electron-spin/nuclear-spin interactions in semiconductors are summarized by putting emphasis on dynamical nuclear-spin polarization and detection achieved by using electrical means. These have been demonstrated in quantum dots in the spin-blockade regime, edge channel in the integer quantum-Hall-effect regime and bulk in the fractional quantum-Hall-effect regime. The electron-spin/nuclear-spin interactions, especially at the spin transition point of nu = 2/3 fractional filling, result in an almost linear relationship between nuclear-spin magnetization and the resistance value. As the nuclear-spin magnetization can be measured for a single layer and even for nanostructures by just measuring the resistance, the powerful features of nuclear magnetic resonance can be successfully applied to semiconductor quantum wells, bilayers and point-contact structures where characteristics are well controlled by gates. In GaAs point-contact devices, full coherent control of a quantum four-level system has been demonstrated for I = 3/2 As and Ga nuclei toward nuclear-spin-based quantum information processing. Multiple quantum coherence was clearly observed reflecting the direct detection of nuclear-spin magnetization. In quantum wells and bilayer systems, novel electron-spin features, such as spin texture, a canted spin state and related low-frequency spin fluctuations arising from the breakdown of planar symmetry, have been sensitively detected by using nuclear-spin-based measurements. We also discuss electron-spin fluctuations originating from spin-orbit interactions observed via a nuclear relaxation experiment and the characterization of the nanoscale strain obtained through quadrupolar splitting. Finally, a possible extension of nuclear-spin manipulation and nuclear-spin-based measurements is briefly discussed.

 

16.    Y. Homma, H. P. Liu, D. Takagi, and Y. Kobayashi

            "Single-Walled Carbon Nanotube Growth with Non-Iron-Group "Catalysts" by Chemical Vapor Deposition"

            Nano Research 2 (10)793-799 (2009).

 

            ABSTRACT: Various materials have been found to "catalyze" carbon nanotube growth in chemical vapor deposition (CVD) when they become nano-sized particles. These involve not only metals, such as Pd, Pt, Au, Ag, and Cu, but also semiconductors, such as Si, Ge, and SiC. Alumina and diamond nanoparticles also produce carbon nanotubes. These "catalysts", which are better called "seeds", can be categorized into two types: one type forms a eutectic liquid or highly-mobile alloy with carbon, and carbon atoms precipitate from the eutectic alloy; the other type remains as a solid phase and form a carbon surface layer during CVD growth. In this paper, we review recent studies of SWCNT growth with these non-iron-group materials and highlight the mechanisms involved.

 

17.    Y. Homma, S. Chiashi, and Y. Kobayashi

            "Suspended single-wall carbon nanotubes: synthesis and optical properties"

            Reports On Progress In Physics 72 (6), 066502 (2009).

 

            ABSTRACT: A single-wall carbon nanotube (SWNT) is a rolled-up graphene sheet, and all the carbon atoms are in the surface layer. Thus, when lying on the substrate surface, or forming a bundle, SWNTs suffer from strong interaction with the substrate atoms or other nanotubes. However, when a SWNT is suspended between mesa structures, the interactions with the substrate and other nanotubes are minimized, which is important for extracting the intrinsic properties of nanotubes. In this paper, we review the synthesis of suspended SWNTs between mesa structures and their optical properties. The first part focuses on the growth and characterization of suspended SWNTs, the mechanisms of suspended structure formation and control of the structures (individual or bundled). The second part describes photoluminescence and Raman spectroscopy of individual and ensemble SWNTs. Highly enhanced photoluminescence and Raman signals enable us to examine the structure of individual SWNTs. The third part describes device applications of suspended SWNTs.

 

18.    T. Honjo, A. Uchida, K. Amano, K. Hirano, H. Someya, H. Okumura, K. Yoshimura, P. Davis, and Y. Tokura

            "Differential-phase-shift quantum key distribution experiment using fast physical random bit generator with chaotic semiconductor lasers"

            Optics Express 17 (11)9053-9061 (2009).

 

            ABSTRACT: A high speed physical random bit generator is applied for the first time to a gigahertz clocked quantum key distribution system. Random phase-modulation in a differential-phase-shift quantum key distribution (DPS-QKD) system is performed using a 1-Gbps random bit signal which is generated by a physical random bit generator with chaotic semiconductor lasers. Stable operation is demonstrated for over one hour, and sifted keys are successfully generated at a rate of 9.0 kbps with a quantum bit error rate of 3.2% after 25-km fiber transmission. (C) 2009 Optical Society of America

 

19.    C. Hufnagel, T. Mukai, and F. Shimizu

            "Stability of a superconductive atom chip with persistent current"

            Physical Review A 79 (5), 053641 (2009).

 

            ABSTRACT: The lifetime of Rb-87 atoms trapped in a z wire trap generated by a closed-circuit superconductive current on a MgB2 strip is measured as a function of the distance between the atom and the strip. The lifetime is found to be longer than 10 s at a distance of 40 mu m. This value is an order of magnitude longer than the lifetime of a trap generated by a normal current at the same distance. However, it is many orders of magnitude shorter than the theoretical decay rate induced by the spin-flip transition caused by the fluctuation of the current. This shows that for a type-II superconductor the dominant trap loss mechanism is not the spin-flip transition caused by noise as with a normal current atom trap. An analysis of our measurement suggests that magnetic field distortion resulting from flux penetration into the superconductor leads to much faster decay.

 

20.    H. Ichikawa, Y. Kobayashi, T. Sakuraba, H. Shibata, and A. Matsuda

            "Impurity effect on superconducting gap and pseudogap"

            Physica C-superconductivity And Its Applications 469 (15-20)1013-1015 (2009).

 

            ABSTRACT: Co substituted Bi2212 samples of Bi2.1Sr1.9Ca(Cu1-xCox)O8+delta, (x=0, 0.01, 0.02, 0.04, 0.06, and Tc = 85,71,52,35 K) were prepared, and their electronic density states were characterized by a low temperature STM. The experimental results revealed that superconducting gap-like features were rapidly destroyed, while pseudogap-like features were enhanced with increasing impurities, suggesting that the origin of the pseudogap is different from that of a superconducting gap. We suggested a two phase-like model to explain the behavior of a gap map and a gap distribution function. On the other hand, spatial gap and pseudogap inhomogeneity persisted in all Co concentrations. This indicates that the origin of inhomogeneity is not related to in-plane disorder or impurities. (C) 2009 Elsevier B.V. All rights reserved.

 

21.    K. Inaba, and S. Suga

            "Finite-temperature properties of attractive three-component fermionic atoms in optical lattices"

            Physical Review A 80 (4), 041602 (2009).

 

            ABSTRACT: We investigate the finite-temperature properties of attractive three-component (colors) fermionic atoms in optical lattices using a self-energy functional approach. As the strength of the attractive interaction increases in the low-temperature region, we observe a second-order transition from a Fermi liquid to a color superfluid (CSF), where atoms from two of the three colors form Cooper pairs. In the strong attractive region, we observe a first-order transition from a CSF to a trionic state, where three atoms with different colors form singlet bound states. A crossover between a Fermi liquid and a trionic state is observed in the high-temperature region. We present a phase diagram covering zero to finite temperatures. We demonstrate that the CSF transition temperature is enhanced by the anisotropy of the attractive interaction.

 

22.    Y. Iwai, T. Honjo, K. Inoue, H. Kamada, Y. Nishida, O. Tadanaga, and M. Asobe

            "Polarization-independent, differential-phase-shift, quantum-key distribution system using upconversion detectors"

            Optics Letters 34 (10)1606-1608 (2009).

 

            ABSTRACT: We propose and demonstrate a polarization-independent, differential-phase-shift, quantum-key distribution system with upconversion detectors. Even though the detectors have polarization dependency, use of alternative polarization modulation and a two-bit delay interferometer achieves polarization-insensitive operation. In an experiment, sifted key bits were polarization-independently generated over 50 km fiber. (C) 2009 Optical Society of America

 

23.    G. H. Jeong, S. Suzuki, and Y. Kobayashi

            "Synthesis and characterization of Au-attached single-walled carbon nanotube bundles"

            Nanotechnology 20 (28), 285708 (2009).

 

            ABSTRACT: We synthesized suspended single-walled carbon nanotubes (SWNTs) by the thermal chemical vapor deposition method and functionalized them with Au nanoparticles (NPs). We used 3-(aminopropyl) triethoxysilane as a linker and controlled the Au NP density on the SWNT surface by changing the reaction time. In the Raman scattering spectra of the Au-functionalized SWNTs, an enhanced peak frequency and peak intensity were observed in the non-resonant region. A significant enhancement of the metallic character in the high frequency region was also observed, especially when we used a 633 nm laser. By measuring the electric properties using a standard field effect transistor configuration, we found that charge transfer occurred during the functionalization processes. It is expected that the charge transfer related optical enhancement may affect the observed change in the Raman profiles.

 

24.    G. H. Jeong, and Y. Kobayashi

            "Different Behaviors of Catalytic Nanoparticles during Carbon Nanotube Growth by Chemical Vapor Deposition"

            Journal Of The Korean Physical Society 54 (3)1011-1015 (2009).

 

            ABSTRACT: We report different behaviors of catalytic nanoparticles during thermal chemical vapor deposition (CVD) growth of single-walled carbon nanotubes (SWNTs). We used iron and cobalt nanoparticles (NPs) as catalysts and systematically investigated their structural and compositional evolution before and after the CVD process. In the case of iron NPs, we observed particle embedment into the substrates, which caused a decrease in the apparent height oil atomic force microscope measurements. The mean size of the Co NPs was also reduced due mainly to the evaporation, which was clearly measured by using X-ray photoelectron spectroscopy and secondary ion mass spectroscopy.

 

25.    H. Kageshima, and M. Kasu

            "Origin of Schottky Barrier Modification by Hydrogen on Diamond"

            Japanese Journal Of Applied Physics 48 (11), 111602 (2009).

 

            ABSTRACT: The origin of the Schottky barrier modification on diamond (100) surfaces by hydrogen is studied based or, simplified interface models with the first-principles calculation It is revealed that the estimated S-factor is rather negative for the ideal contact with no interfacial dangling bonds, while it approaches 1 when the interface is terminated by just hydrogen The negative S-factor is thought to come from the formation of interfacial chemical bonds between the metal, and the diamond It is suggested that hydrogen-termination prevents such interfacial bond formation and makes the general metal induced gap state theory work, as well as passivates the interfacial dangling bond states which are the strong sources of the pinning of the Schottky barrier height. (C) 2009 The Japan Society of Applied Physics

 

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

            "Theoretical Study of Epitaxial Graphene Growth on SiC(0001) Surfaces"

            Applied Physics Express 2 (6), 065502 (2009).

 

            ABSTRACT: The epitaxial graphene growth mechanism on SiC(0001) surfaces is studied based on the energetics via the first-principles calculation. It is found that a Si terminated surface is important for the epitaxial growth of thin flat graphene sheets. This surface encourages the growth of graphene sheets because the surface Si atoms act as catalyst. Si desorbed sites trap excess C atoms, and form graphene islands. It is also found that the new graphene sheet prefers to grow just on the Si terminated surface of the SiC substrate even if the surface is covered with other graphene sheets. (c) 2009 The Japan Society of Applied Physics

 

27.    T. Kaizawa, M. Arita, A. Fujiwara, K. Yamazaki, Y. Ono, H. Inokawa, Y. Takahashi, and J. B. Choi

            "Single-Electron Device With Si Nanodot Array and Multiple Input Gates"

            Ieee Transactions On Nanotechnology 8 (4)535-541 (2009).

 

            ABSTRACT: We have developed a flexible-logic-gate singleelectron device (SED) with an array of nanodots. Although the small size of SEDs is highly advantageous, the size of the nanodots inevitably fluctuates, which causes variations in device characteristics. This variability can be eliminated and high device functionality can be obtained by exploiting the oscillatory characteristics and multigate capability of SEDs. We fabricated, on a silicon-on-insulator wafer, a Si nanodot array device with two input gates and a control gate and investigated its basic operation characteristics experimentally. The device was demonstrated to operate as a logic gate providing six important logic functions (AND, OR, NAND, NOR, XOR, and XNOR), which are obtained by adjusting the control-gate voltage.

 

28.    H. Kamata, T. Ota, and T. Fujisawa

            "Correlation Measurement of Time-Dependent Potentials in a Semiconductor Quantum Point Contact"

            Japanese Journal Of Applied Physics 48 (4), 04C149 (2009).

 

            ABSTRACT: A novel time-correlation measurement technique is proposed and demonstrated to investigate time-dependent potentials in nanostructures. We focus on a semiconductor quantum point contact, in which the tunneling barrier potential and the source-drain bias potential can be independently controlled by external voltage pulses. Time-correlation of the two potentials is obtained by measuring the dc current at various time differences between the two pulses. The observed correlation function is consistent with the model and can be used to evaluate the waveform of the time-dependent potential. (C) 2009 The Japan Society of Applied Physics

 

29.    N. Kasai, A. Shimada, T. Nyberg, and K. Torimitsu

            "An Electrochemical Sensor Array and Its Application to Real-Time Brain Slice Imaging"

            Electronics And Communications In Japan 92 (9)1-6 (2009).

 

            ABSTRACT: An electrochemical sensing system using a planar microelectrode array has been developed for monitoring biological molecules with relatively high spatial and temporal resolution. This allows noninvasive real-time imaging of biological molecules released from tissue. In this study, we establish a multichannel hydrogen peroxide (H2O2) sensing system to monitor the real-time H2O2 distribution in tissue using a planar sensor array. H2O2 is known to be associated with the pathology of neurological diseases because it is a by-product of degenerative reactions involving reactive oxygen species, which are a major cause of oxidative stress in mammalian cells. The sensor array is based on a 64-channel ITO electrode array composed of 50 x 50 mu m electrodes modified with an enzyme (horseradish peroxidase) and an electron transfer mediator. We place a cultured rat hippocampal slice on the array and measure the current at each sensor using a multipotentiostat. When we introduce bicuculline into the solution as a stimulant in the presence of a catalase inhibitor, we can observe a distinct increase in the H2O2 concentration. This real-time H2O2 distribution monitoring system is a powerful tool with which to explore the neuronal cell death mechanism in biological systems. (C) 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 92(9): 1-6, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10140

 

30.    T. Kasai, H. Nakajima, T. Fujii, I. Terasaki, T. Watanabe, H. Shibata, and A. Matsuda

            "High-T-c superconductor near the S-I transition"

            Physica C-superconductivity And Its Applications 469 (15-20)1016-1019 (2009).

 

            ABSTRACT: We report on the density of states measurements of Bi2212 (Bi2+xSrCaCu2O8+delta) near the superconductivity-insulator transition using a low temperature scanning tunneling microscope. We prepared highly underdoped Bi rich Bi2212 single crystals (T-c similar to 32 K). The energy gap distribution did not provide an energy scale proportional to T-c. Averaged tunnel spectra with various doping levels were scaled into a single line if energy was normalized by their respective gap values. This indicated there was no crossover energy, which separates a pseudogap and a superconducting gap. (C) 2009 Elsevier B.V. All rights reserved.

 

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

            "Structural and Electrical Properties of Organic Conducting Polymers Bearing Tetrathiafulvalene Backbone"

            Molecular Crystals And Liquid Crystals 504231-237 (2009).

 

            ABSTRACT: The structural and electrical properties of a new organic conducting polymer bearing a tetrathiafulvalene backbone whose termini are capped with the thioacetyl group were investigated. AFM observations indicated that on a gold surface, the polymers form rigid rod-like structures with a stretched length of about 50 nm, which is comparable to its average length (similar to 60 nm). The current-voltage characteristic exhibited semiconducting behavior with a conductivity of 1.0 x 10(-5) Scm(-1). A doping measurement was also performed using iodine. The current was enhanced 10(2)-10(4) times after doping indicating the highly electron-donating nature of the polymer.

 

32.    K. Kato, A. Ishizawa, K. Oguri, K. Tateno, T. Tawara, H. Gotoh, M. Kitajima, and H. Nakano

            "Anisotropy in Ultrafast Carrier and Phonon Dynamics in p-Type Heavily Doped Si"

            Japanese Journal Of Applied Physics 48 (10), 100205 (2009).

 

            ABSTRACT: We performed time-resolved reflectivity measurements in p-type heavily doped Si under non-resonant excitation. A large contribution from anisotropic state-filling is observed, indicating that the lowered Fermi energy due to the p-type heavy doping enhances the anisotropy in the hole distribution. The initial phase shift of coherent phonons induced by p-type doping is attributed to the anisotropic hole distribution. (C) 2009 The Japan Society of Applied Physics

 

33.    M. A. Khalafalla, Y. Ono, K. Nishiguchi, and A. Fujiwara

            "Horizontal position analysis of single acceptors in Si nanoscale field-effect transistors"

            Applied Physics Letters 94 (22), 223501 (2009).

 

            ABSTRACT: The authors performed conductance measurements to identify the horizontal position of single boron acceptors in silicon-on-insulator nanoscale field-effect transistors at a temperature of 6 K. The horizontal position, i.e., how far the acceptor is from the source or drain terminal, is qualitatively obtained, and it is shown, on the level of single dopants, that the acceptor near the source significantly affects the subthreshold nature of the transistor.

 

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

            "The interplay between one-dimensional confinement and two-dimensional crystallographic anisotropy effects in ballistic hole quantum wires"

            New Journal Of Physics 11, 043018 (2009).

 

            ABSTRACT: In this paper, we study the Zeeman spin-splitting in hole quantum wires aligned along the [(2) over bar 33] and [01 (1) over bar] crystallographic axes of a high-mobility (311) A undoped AlGaAs/GaAs heterostructure. We obtained measurements of the effective g-factor g* as a function of the wire width for in-plane magnetic fields aligned both parallel and perpendicular to the wire axis. We interpret our data in terms of a qualitative model that involves the interplay of two effects-1D confinement and 2D crystalline anisotropy.

 

35.    T. Kodera, K. Ono, Y. Kitamura, Y. Tokura, Y. Arakawa, and S. Tarucha

            "Quantitative Estimation of Exchange Interaction Energy Using Two-Electron Vertical Double Quantum Dots"

            Physical Review Letters 102 (14), 146802 (2009).

 

            ABSTRACT: We use Pauli-spin blockade in two-electron vertical double quantum dots to quantitatively estimate the exchange energy J in a wide range of interdot level detuning Delta and fully compare it with calculations. Pauli-spin blockade is lifted via a singlet- (S-)triplet (T) transition mediated by hyperfine coupling, which abruptly occurs in our devices when the S-T transition energy or J is compensated by the Zeeman energy. We use this feature to derive J depending on Delta between the S-S and T-T resonances. The obtained J versus Delta including the resonance effect is perfectly reproduced by Hubbard model calculations.

 

36.    H. Kubota, S. Kawanishi, and M. Notomi

            "Simple analysis of water-filled hollow-core silica photonic bandgap fiber"

            Ieice Electronics Express 6 (12)870-875 (2009).

 

            ABSTRACT: We performed a simple numerical investigation of a silica hollow core photonic bandgap fiber whose core area was filled with water. We propose cladding parameters for the PBF designed to obtain a photonic bandgap of broader than 200 nm at a center wavelength of 500 nm.

 

37.    M. Kubovic, and M. Kasu

            "Improvement of Hydrogen-Terminated Diamond Field Effect Transistors in Nitrogen Dioxide Atmosphere"

            Applied Physics Express 2 (8), 086502 (2009).

 

            ABSTRACT: The electrical properties of field effect transistors (FETs) fabricated on hydrogen-terminated diamond have been greatly improved by exposing the diamond surface to nitrogen dioxide. Exposure to NO2 gas significantly increased the hole sheet charge density up to 1.3 x 10(14) cm(-2), which is several times higher than previously reported values. FETs exposed to NO2 gas exhibited lower source and drain resistances, which facilitated a 1.8 fold increase in maximum drain current, transconductance increased 1.5 times and power gain cut-off frequency increased 1.6 times. (C) 2009 The Japan Society of Applied Physics

 

38.    M. Kubovic, M. Kasu, Y. Yamauchi, K. Ueda, and H. Kageshima

            "Structural and electrical properties of H-terminated diamond field-effect transistor"

            Diamond And Related Materials 18 (5-8)796-799 (2009).

 

            ABSTRACT: A dielectric barrier separating hydrogen induced p-type channel and Al gate metal contact of diamond FET has been investigated. The separation barrier is necessary to prevent tunneling current between the H-induced channel and the gate contact. In this investigation, CV measurements, fitting of forward IV characteristics, TEM and SIMS profiles have been used to obtain a more detailed picture of this barrier layer. While the composition of this layer is not clear, TEM and SIMS measurements indicate that this layer may be connected to a diamond phase or aluminium oxide. Using material properties of these materials, thickness of the separation layer extracted from the CV measurements was between 5-10 nm and the channel sheet change density was above 1 x 10(13) cm(-2). This thickness is in good agreement with the TEM observations. Frequency dependent CV measurements showed almost no frequency dependence, and no UV light dependence has been observed. Temperature dependent CV measurements showed a decrease of the dielectric constant at 100 degrees C. Fitting of the forward tunnelling current indicated a thickness of the barrier layer of about 5 nm with a barrier height of 2.4 eV. (C) 2009 Elsevier B.V. All rights reserved.

 

39.    K. Kumakura, and T. Makimoto

            "High-temperature characteristics up to 590 degrees C of a pnp AlGaN/GaN heterojunction bipolar transistor"

            Applied Physics Letters 94 (10), 103502 (2009).

 

            ABSTRACT: We investigated the temperature dependence of the common-emitter I-V characteristics of a pnp AlGaN/GaN heterojunction bipolar transistor (HBT) at temperatures ranging from RT to 590 degrees C. The HBT operated at 590 degrees C in air with a current gain of 3. Even at 590 degrees C, the collector-emitter leakage current was as low as 9 mu A at the collector-emitter voltage of 40 V. Although there is no significant degradation of the HBT characteristics only by annealing in air at 400 degrees C for 2 h, the current gain reduced to 30% of the initial one after the common-emitter operation at 400 degrees C for 2 h.

 

40.    R. A. Leute, M. Feneberg, R. Sauer, K. Thonke, S. B. Thapa, F. Scholz, Y. Taniyasu, and M. Kasu

            "Photoluminescence of highly excited AlN: Biexcitons and exciton-exciton scattering"

            Applied Physics Letters 95 (3), 031903 (2009).

 

            ABSTRACT: Low-temperature photoluminescence spectra of nominally undoped high quality AlN layers on SiC and Al2O3 substrates are reported. Under high excitation conditions, we observe several bands that increase superlinearly with the excitation density. Based on temperature and excitation level dependences recorded on different samples, we identify a band 36 meV below the free A-exciton transition as due to exciton-exciton scattering (P-2 band) and a second band down-shifted from the A-exciton transition by 27 meV as due to biexciton recombination. The combined data yield an exciton binding energy of 48 meV.

 

41.    M. Lucamarini, G. Di Giuseppe, and K. Tamaki

            "Robust unconditionally secure quantum key distribution with two nonorthogonal and uninformative states"

            Physical Review A 80 (3), 032327 (2009).

 

            ABSTRACT: We present an unconventional form of decoy-state technique to make the single-photon Bennett 1992 protocol robust against losses and noise of a communication channel. Two uninformative states are prepared by the transmitter in order to prevent the unambiguous state discrimination attack and improve the phase-error rate estimation. The presented method does not require strong reference pulses, additional electronics, or extra detectors for its implementation.

 

42.    I. Mahboob, K. Nishiguchi, A. Fujiwara, and H. Yamaguchi

            "Room temperature piezoelectric displacement detection via a silicon field effect transistor"

            Applied Physics Letters 95 (23), 233102 (2009).

 

            ABSTRACT: An electromechanical oscillator embedded with a two dimensional electron gas is capacitively coupled to a silicon field effect transistor (Si-FET). The piezovoltage induced by the mechanical motion modulates the current passing through the Si-FET enabling the electromechanical oscillator's position to be monitored. When the Si-FET is biased at its optimal point, the motion induced piezovoltage can be amplified resulting in a displacement sensitivity of 6 x 10(-12) mHz(-1/2) for a 131 kHz GaAs resonator which is among the highest recorded for an all-electrical room temperature detection scheme. (C) 2009 American Institute of Physics. [doi:10.1063/1.3271525]

 

43.    H. Maki, T. Mizuno, S. Suzuki, T. Sato, and Y. Kobayashi

            "Multi-Back-Gate Control of Carbon Nanotube Double-Quantum Dot"

            Japanese Journal Of Applied Physics 48 (4), 04C201 (2009).

 

            ABSTRACT: We have fabricated single-walled carbon nanotube (SWNT) quantum dot device with local multi-back gates, in which a SWNT is not surrounded by an insulator or gate electrodes. The charge states of multi-quantum dots, which are separated by an intrinsic defect of a SWNT, can be independently controlled by applying two local back gates. The charge stability diagram changes depending on the gate voltage range, which changes the interdot coupling between two dots. Furthermore, a honeycomb charge stability diagram corresponding to an intermediately coupled double-quantum dot is also observed. (C) 2009 The Japan Society of Applied Physics

 

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

            "Generic phase diagram of "electron-doped" T ' cuprates"

            Physica C-superconductivity And Its Applications 469 (15-20)924-927 (2009).

 

            ABSTRACT: We investigated the generic phase diagram of the electron doped superconductor, Nd2-xCexCuO4, using films prepared by metal organic decomposition. After careful oxygen reduction treatment to remove interstitial O-ap atoms, we found that the T-c increases monotonically from 24 K to 29 K with decreasing x from 0.15 to 0.00, demonstrating a quite different phase diagram from the previous bulk one. The implication of our results is discussed on the basis of tremendous influence of O-ap "impurities" on superconductivity and also magnetism in T' cuprates. Then we conclude that our result represents the generic phase diagram for oxygen-stoichiornetric Nd2-xCexCuO4. (C) 2009 Elsevier B.V. All rights reserved.

 

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

            "Reduction dependence of superconductivity in the end-member T ' cuprates"

            Physica C-superconductivity And Its Applications 469 (15-20)940-943 (2009).

 

            ABSTRACT: We have recently achieved superconductivity in T'-RE2CuO4 (RE: Pr, Nd, Sm, Eu, and Gd), using epitaxial thin films by metal organic decomposition. The key recipes to achieve superconductivity are low-P-O2 firing and subsequent vacuum reduction to minimize the amount of impurity oxygen atoms, which are very harmful to high-T-c superconductivity. In this article, we report our investigation on the reduction dependence Of Superconductivity of T'-RE2CuO4. For thin films, the amount of remnant O-ap atoms is difficult to evaluate but we propose that one good measure for this may be the c-axis lattice constant, which tells us whether the reduction is insufficient or excessive. (C) 2009 Elsevier B.V. All rights reserved.

 

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

            "Synthesis and properties of superconducting T-'-R2CuO4 (R=Pr, Nd, Sm, Eu, Gd)"

            Physical Review B 79 (10), 100508 (2009).

 

            ABSTRACT: The parent compounds of high-T-c cuprates have long been considered to be antiferromagnetic insulators. In this Rapid Communication, however, we report that superconductivity is achieved in T-'-R2CuO4 (R=Pr, Nd, Sm, Eu, Gd). Superconducting T-'-R2CuO4 films were synthesized by using metal-organic decomposition. The highest T-c of T-'-R2CuO4 is over 30 K, substantially higher than "electron-doped" analogs. Remarkably, Gd2CuO4, even the derivatives of which have not shown superconductivity so far, gets superconducting with T-c(onset) as high as similar to 20 K. The implication of our results is briefly discussed.

 

47.    B. Miquel, and H. Takesue

            "Observation of 1.5 mu m band entanglement using single photon detectors based on sinusoidally gated InGaAs/InP avalanche photodiodes"

            New Journal Of Physics 11, 045006 (2009).

 

            ABSTRACT: We describe the application of single photon detectors based on InGaAs/InP avalanche photodiodes incorporating the sinusoidal gating technique into a 1.5 mu m band entanglement measurement. We constructed two detectors based on this technique with a 500 MHz gate frequency. Using these detectors, we successfully demonstrated the high-speed and high signal-to-noise ratio observation of 1.5 mu m-band time-bin entangled photon pairs.

 

48.    F. F. Miranda, K. Iwasaki, S. Akashi, K. Sumitomo, M. Kobayashi, I. Yamashita, J. R. Tame, and J. G. Heddle

            "A Self-Assembled Protein Nanotube with High Aspect Ratio"

            Small 5 (18)2077-2084 (2009).

 

            ABSTRACT: Production of a self-assembled protein nanotube achieved through engineering of the 11mer ring protein trp RNA-binding attenuation protein is described. The produced mutant protein is able to stack in solution to produce an extremely narrow, uniform nanotube apparently stabilized by a mixture of disulfide bonds and hydrophobic interactions. Assembly is reversible and the length of tube can potentially be controlled. Large quantities of hollow tubes 8.5 nm in overall diameter with lengths varying from 7 nm to over 1 mu m are produced. The structure is analyzed using transmission electron microscopy, atomic force microscopy, mass spectrometry, and single-particle analysis and it is found that component rings stack in a head-to-head fashion. The internal diameter of the tube is 2.5 nm, and the amino acid residues lining the central cavity can be mutated, raising the possibility that the tube can be filled with a variety of conducting or semiconducting materials.

 

49.    H. Morishita, L. S. Vlasenko, H. Tanaka, K. Semba, K. Sawano, Y. Shiraki, M. Eto, and K. M. Itoh

            "Electrical detection and magnetic-field control of spin states in phosphorus-doped silicon"

            Physical Review B 80 (20), 205206 (2009).

 

            ABSTRACT: Electron paramagnetic resonance of ensembles of phosphorus donors in silicon has been detected electrically with externally applied magnetic fields lower than 200 G. Because the spin Hamiltonian was dominated by the contact hyperfine term rather than by the Zeeman terms at such low magnetic fields, superposition states alpha vertical bar up down arrow > + beta vertical bar down arrow up arrow > and -Chi vertical bar up down arrow > + alpha vertical bar down arrow up arrow > were formed between phosphorus electron and nuclear spins, and electron paramagnetic resonance transitions between these superposition states and vertical bar up arrow up arrow > and vertical bar down arrow down arrow > states are observed clearly. A continuous change of alpha and beta with the magnetic field was observed with a behavior fully consistent with theory of phosphorus donors in silicon.

 

50.    K. Muraki, P. Giudici, and N. Kumada

            "SPIN EFFECTS IN THE PHASE TRANSITION OF THE nu(T)=1 BILAYER ELECTRON SYSTEM"

            International Journal Of Modern Physics B 23 (12-13)2587-2595 (2009).

 

            ABSTRACT: We present tilted-field experiments on a bilayer electron system at nu(T) = 1 with negligible tunneling and demonstrate that the spin degree of freedom plays a decisive role in the ground-state phase diagram of the system. We observe that the phase boundary separating the incompressible quantum Hall state and a compressible state at d/l(B) = 1.90 (d: interlayer distance, l(B): magnetic length) in a perpendicular field shifts to higher densities with tilt until it saturates at d/l(B) = 2.33. We develop a model describing the energies of the competing phases and show that the observed shift of the phase boundary reflects the spin-polarization dependence of the Coulomb and Zeeman energies of the compressible state. A new phase diagram as a function of d/l(B) and the Zeeman energy is established and its implications as to the nature of the phase transition are discussed.

 

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

            "Local conductance measurements of double-layer graphene on SiC substrate"

            Nanotechnology 20 (44), 445704 (2009).

 

            ABSTRACT: The microscopic structural and electrical properties of few-layer graphene grown on an SiC substrate were characterized by low-energy electron microscopy, transmission electron microscopy and scanning probe microscopy measurements of local conductance. The double-layer graphene sheet was confirmed to be continuous across the atomic steps on the buried SiC substrate surface, and the measured local conductance was clearly modified in the vicinity of the steps. The conductance decreased ( slightly increased) at the lower ( upper) side of the steps, suggesting deformation-induced strain is the origin of the conductance modification. From the contact force dependence of the conductance images, the effective contact areas for both nanogap-probe and point-probe measurements were estimated.

 

52.    H. Nakano, S. Saito, K. Semba, and H. Takayanagi

            "Quantum Time Evolution in a Qubit Readout Process with a Josephson Bifurcation Amplifier"

            Physical Review Letters 102 (25), 257003 (2009).

 

            ABSTRACT: We analyzed the Josephson bifurcation amplifier (JBA) readout process of a superconducting qubit quantum mechanically by calculating the dynamics of the density operator of a driven nonlinear oscillator and a qubit coupled system during the measurement process. In purely quantum cases, bifurcation is impossible. Introducing decoherence enables us to reproduce the bifurcation with a finite hysteresis. When a qubit is initially in a superposition state, we have observed the qubit-probe (JBA) entangled state, and it is divided into two separable states at the moment the JBA transition begins. This corresponds to "projection." To readout the measurement result, however, we must wait until the two JBA states are macroscopically well separated. The waiting time is determined by the strength of the decoherence in the JBA.

 

53.    Y. Niida, K. Takashina, A. Fujiwara, T. Fujisawa, and Y. Hirayama

            "Spin splitting of upper electron subbands in a SiO2/Si(100)/SiO2 quantum well with in-plane magnetic field"

            Applied Physics Letters 94 (14), 142101 (2009).

 

            ABSTRACT: We observe a lifting of the twofold spin degeneracy of conduction-band electrons in an upper-valley subband with in-plane magnetic field in a SiO2/Si(100)/SiO2 quantum well, which is manifest in a splitting of a feature in the conductivity accompanying the occupation of the upper-valley subband. The splitting increases in proportion to the in-plane magnetic field, allowing the product of the effective g-factor and effective mass g(*)m(*) to be obtained. The value remains constant over wide ranges of valley splitting, total electron density, and potential bias.

 

54.    K. Nishiguchi, N. Clement, T. Yamaguchi, and A. Fujiwara

            "Si nanowire ion-sensitive field-effect transistors with a shared floating gate"

            Applied Physics Letters 94 (16), 163106 (2009).

 

            ABSTRACT: Ion-sensitive field-effect transistors (ISFETs) arrayed in parallel were fabricated on a silicon-on-insulator substrate. Since the nanoscale wire channels of the ISFETs are bridged with a floating gate on which molecules are preferably immobilized, signals originating from charged materials only on the floating gate can appear and can therefore be distinguished from background noise, which leads to noise-robust sensing. Additionally, the nanoscale channels provide the ISFETs with single-electron-resolution charge sensitivity as well as a reduction in background noise induced in the wider channels used as electrical leads. These features promise the detection of a small number of molecules.

 

55.    K. Nishiguchi, and A. Fujiwara

            "Single-electron counting statistics and its circuit application in nanoscale field-effect transistors at room temperature"

            Nanotechnology 20 (17), 175201 (2009).

 

            ABSTRACT: A circuit utilizing single electrons is demonstrated at room temperature. Individual electrons randomly passing through the nanoscale silicon-on-insulator metal-oxide-semiconductor field-effect transistor (MOSFET) are monitored by an electrometer in real time. Such a random behavior of single electrons is used for high-quality random-number generation suitable for data processing which stochastically extracts the most preferable pattern among various ones. MOSFET-based random-number generation allows fast operation as well as high controllability, which leads to flexible extraction of the preferable pattern.

 

56.    A. Nishikawa, K. Kumakura, M. Kasu, and T. Makimoto

            "Low-temperature characteristics of the current gain of GaN/InGaN double-heterojunction bipolar transistors"

            Journal Of Crystal Growth 311 (10)3000-3002 (2009).

 

            ABSTRACT: We investigated the temperature dependence of the current gain of npn-type GaN/InGaN double-heterojunction bipolar transistors (DHBTs) in the low-temperature region. The current gain increased with decrease in device temperature due to the reduction of the recombination current in the p-type base layer. The current gain reached as high as 5000 at 40 K, which is the highest among nitride-based HBTs. For conventional HBTs made of InP or GaAs, the current gain decreased with decreasing device temperature. However, no reduction of the current gain was observed in this study, suggesting that the minority carrier mobility in the p-type InGaN base layer has negative temperature dependence, presumably because the ionized impurity scattering is relatively unaffected owing to the carrier freezeout and the high activation energy of Mg in the p-InGaN base layer. (C) 2009 Elsevier B.V. All rights reserved.

 

57.    T. Nishikawa, A. Ozawa, Y. Nishida, M. Asobe, F. L. Hong, and T. W. Hansch

            "Efficient 494 mW sum-frequency generation of sodium resonance radiation at 589 nm by using a periodically poled Zn:LiNbO3 ridge waveguide"

            Optics Express 17 (20)17792-17800 (2009).

 

            ABSTRACT: A solid-state-laser based single-frequency 589 nm light source that can be easily used in the laboratory is needed for sodium spectroscopy studies and cold sodium atom experiments. This paper shows that by using a periodically poled Zn-doped LiNbO3 ridge waveguide for sum-frequency generation, we can obtain a high conversion efficiency to 589 nm light from two sub-watt 1064 and 1319 nm Nd:YAG lasers via a simple single pass wavelength conversion process without employing an enhancement cavity. A 494 mW light at 589 nm is generated and achieves overall conversion efficiency from the laser power of 41%. Excellent long-term stability of output power is obtained and its standard deviation is characterized to be 0.09%. (C) 2009 Optical Society of America

 

58.    J. Nitta, T. Bergsten, Y. Kunihashi, and M. Kohda

            "Electrical manipulation of spins in the Rashba two dimensional electron gas systems"

            Journal Of Applied Physics 105 (12), 122402 (2009).

 

            ABSTRACT: We present our theoretical and experimental studies on manipulation of electron spins based on the Rashba spin-orbit interaction (SOI) in semiconductor heterostructures. Quantum well (QW) thickness dependence of the Rashba SOI strength alpha is investigated in InP/InGaAs/InAlAs asymmetric QWs by analyzing weak antilocalization. Two different QW thicknesses show inverse N-s dependence of vertical bar alpha vertical bar in the same heterostructures. This inverse N-s dependence of vertical bar alpha vertical bar is explained by the k.p perturbation theory. We confirm that narrow wires are effective to suppress the spin relaxation. Spin interference effects due to spin precession are experimentally studied in small array of mesoscopic InGaAs rings. This is an experimental demonstration of a time reversal Aharonov-Casher effect, which shows that the spin precession angle in an InGaAs channel can be controlled by an electrostatic gate. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3117232]

 

59.    K. Nonaka, K. Tamaru, M. Nagase, H. Yamaguchi, S. Warisawa, and S. Ishihara

            "Evaluation of Thermal-Mechanical Vibration Amplitude and Mechanical Properties of Carbon Nanopillars Using Scanning Electron Microscopy"

            Japanese Journal Of Applied Physics 48 (6), 06FG07 (2009).

 

            ABSTRACT: We describe a method for evaluating thermal-mechanical vibration amplitude by means of analysis of scanning electron microscopy images. The samples used were carbon nanopillars of different heights grown by focused-ion-beam-induced chemical vapor deposition. The secondary electron yield profile of carbon nanopillars excited by thermal noise is modeled, and vibration amplitude is:determined,by fitting the modeled profile to the experimental profile. The Young's modulus of carbon nanopillars is deduced from the determined amplitude. Furthermore, the density of carbon nanopillars is estimated from the deduced Young's modulus and the measured resonant frequency. The obtained Young's moduli and densities range from 51 to 78 GPa and from 2500 to 3500 kg/m(3), respectively. (C) 2009 The Japan Society of Applied Physics

 

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

            "Dynamics of femtosecond laser ablation studied with time-resolved x-ray absorption fine structure imaging"

            Physical Review B 79 (14), 144106 (2009).

 

            ABSTRACT: We studied the dynamics of the femtosecond laser ablation of aluminum in an energy range well above the ablation threshold with the ultrafast time-resolved x-ray-absorption fine structure imaging technique. Analyzing the spectral structures near the L absorption edge that appeared in one-dimensional images of soft-x-ray absorbance, we successfully identified doubly and singly charged ions, neutral atoms, liquid nanoparticles, and possible atomic clusters in the expanding ablation plume. We also clarified that the ejected particles depend strongly on the laser irradiation intensity. The spatiotemporal evolution of the ablation particles allows us to estimate the spatial distribution of atomic density and the ejection velocity of each type of particle. In particular, we discuss the temporal sequence of the particle ejection in the early stages of plume expansion. Our experimental results strongly support the idea that photomechanical fragmentation and vaporization are dominant mechanisms for the production of liquid nanoparticles and neutral atoms, respectively, in femtosecond laser ablation induced in an irradiation intensity range of 10(14)-10(15) W/cm(2).

 

61.    H. Okamoto, T. Kamada, K. Onomitsu, I. Mahboob, and H. Yamaguchi

            "Optical Tuning of Coupled Micromechanical Resonators"

            Applied Physics Express 2 (6), 062202 (2009).

 

            ABSTRACT: Frequency tuning of two mechanically coupled microresonators by laser irradiation is demonstrated. The eigenfrequency of a doubly clamped GaAs beam shifts downward in proportion to laser power due to optically induced thermal stress, which modifies the spring constant of the resonator. This frequency tuning enables the control of the coupling efficiency and thus the realization of perfect coupling between the micromechanical resonators, i.e., purely symmetric and anti-symmetric coupled vibration. This optical tuning is a valuable method for the study of physics in coupled resonators as well as for expanding the applications of micromechanical resonators for sensors, filters, and logics. (C) 2009 The Japan Society of Applied Physics

 

62.    H. Okamoto, D. Ito, K. Onomitsu, T. Sogawa, and H. Yamaguchi

            "Controlling Quality Factor in Micromechanical Resonators by Carrier Excitation"

            Applied Physics Express 2 (3), 035001 (2009).

 

            ABSTRACT: The quality factor (Q-factor) of GaAs microcantilevers; consisting of Si-doped and undoped GaAs layers can be controlled by tuning the wavelength of the incident laser used for carrier excitation. With laser irradiation to [110]-oriented cantilevers at near-absorption-edge wavelengths, the Q-factor increases with increasing the laser power, whereas shorter-wavelength irradiation decreases the Q-factor. We observed the opposite laser power dependence for [(1) over bar 10]-oriented cantilevers. These results suggest the Q-control is due to the piezoelectric stress generated by the photovoltaic effect. (C) 2009 The Japan Society of Applied Physics

 

63.    J. Okuma, N. Hayashi, A. Fujisawa, M. Mitsunaga, and K. Harada

            "Parametric oscillation in sodium vapor by using an external cavity"

            Optics Letters 34 (5)698-700 (2009).

 

            ABSTRACT: We report on parametric oscillation in sodium atomic vapor by using an external cavity. Output powers of similar to 56 mW are obtained for both the signal and idler waves with the input coupling power of 290 mW, resulting in a conversion efficiency of 39%. The signal and idler frequencies are either upshifted or downshifted from the coupling frequency by the amount of the Na hyperfine splitting frequency, and the two waves are found to be strongly temporally correlated. (C) 2009 Optical Society of America

 

64.    H. Omi, T. Kawamura, Y. Kobayashi, S. Fujikawa, Y. Tsusaka, Y. Kagoshima, and J. Matsui

            "Real-Time Analyses of Strain in Ultrathin Silicon Nanolayers on Insulators during Thermal Oxidation"

            Applied Physics Express 2 (12), 126503 (2009).

 

            ABSTRACT: In-plane strain in ultrathin silicon nanolayers of separation by implantation of oxygen wafers was characterized in real time by the grazing incidence X-ray diffraction during thermal oxidation in a newly developed oxidation furnace. The strain in the ultrathin silicon nanolayer during the growth is on the order of 10(-4). The amount of strain does not change for the thicknesses of 6 nm to about 2 nm, but it increases twofold at the thicknesses of less than 2 nm at the oxidation temperature of 1220 degrees C. The strain originates from the volume difference between the Si nanolayers and SiO2. (C) 2009 The Japan Society of Applied Physics DOI: 10.1143/APEX.2.126503

 

65.    H. Omi, H. Kageshima, T. Kawamura, M. Uematsu, Y. Kobayashi, S. Fujikawa, Y. Tsusaka, Y. Kagoshima, and J. Matsui

            "Stability-instability transition of reaction fronts in thermal oxidation of silicon"

            Physical Review B 79 (24), 245319 (2009).

 

            ABSTRACT: By combining atomic force microscopy and x-ray reflectivity measurements, the morphological evolution at the SiO2/Si(001) interface during thermal silicon oxidation was systematically studied as a function of oxidation temperatures. We found that the oxidation-induced roughening switches to smoothening at an oxidation temperature of 1250 degrees C on the oxidation front. The transition is governed by how the strain induced by oxidation is spatially relieved at the interfaces in the silicon oxide bulk film through the interfacial transition layers, which is inevitably important for the strain-relief mechanism.

.

 

66.    K. Oto, R. Inaba, T. Yamada, T. Yamazaki, K. Muro, Y. Hirayama, N. Kumada, and H. Yamaguchi

            "ELECTRON SPIN IMAGING IN QUANTUM HALL DEVICES BY KERR ROTATION MEASUREMENT"

            International Journal Of Modern Physics B 23 (12-13)2750-2754 (2009).

 

            ABSTRACT: The electron spin polarization images in a single layer GaAs/AlGaAs quantum well in the quantum Hall effect (QHE) regime have been observed by using an optical fiber-based high sensitive Kerr rotation microscope. The observed Kerr signal image at the Landau level filling factor nu = 1 reveals the small electron density fluctuation less than 1% through the degree of electron spin polarization. We have also observed the Kerr rotation images in the current flowing QHE devices. At nu = 1 QHE plateau, the winding strip of just nu = 1 incompressible state, which contributes the dissipationless electron transport, has been clearly observed in the bulk region of the devices. The highly current dependent Kerr images have valuable information for studying current density distribution and the distribution of spin polarization in the QHE regime. The experimental results and techniques of the Kerr imaging in the QHE regime have been reported in detail.

 

67.    H. Oyanagi, C. Zhang, A. Tsukada, and M. Naito

            "Lattice Instability in High-Temperature Superconducting Cuprates: Polarons Probed by EXAFS"

            Journal Of Superconductivity And Novel Magnetism 22 (2)165-168 (2009).

 

            ABSTRACT: Lattice instability in the planar Cu-O bond in high-temperature superconducting cuprates is probed by the Cu K-edge extended X-ray absorption fine structure (EXAFS). Refined temperature-dependent polarized EXAFS data for high-quality La1.85Sr0.15CuO4 (LSCO) single crystals grown by MBE and TSFZ methods are analyzed and compared with the transport properties. Temperature-dependent oxygen displacement shows a signature of bond splitting at T (*) and a sharp drop due to superconductivity coherence at T (c). Detailed analysis of the anomalous oxygen displacement demonstrates the Cu-O bond splitting, i.e., long and short bonds (Delta Ra parts per thousand 0.12 A...), which is in good agreement with the recent cluster calculation. The results indicate that the origin of pseudogap is related to the formation of charged dynamical lattice distortions (polarons) that are coexistent with metallic (superconducting) domains.

 

68.    F. Prins, T. Hayashi, B. J. van Steenwijk, B. Gao, E. A. Osorio, K. Muraki, and H. S. van der Zant

            "Room-temperature stability of Pt nanogaps formed by self-breaking"

            Applied Physics Letters 94 (12), 123108 (2009).

 

            ABSTRACT: We present a method to make Pt nanometer-spaced electrodes that are free of metallic particles and stable at ambient conditions. The nanogaps are fabricated using feedback-controlled electromigration to form few-atom contacts. When performing this procedure at elevated temperatures (>420 K), the Pt contacts undergo self-breaking so that nanometer separated electrode pairs are formed. Once cooled down to lower temperatures, the nanogaps stabilize and can be characterized in detail. We find that current-voltage characteristics can be well fitted to a Simmons model for tunneling and gap-size fluctuations at room temperature determined from these fits stay within 0.6 A for at least 50 h.

 

69.    S. Saito, T. Tilma, S. J. Devitt, K. Nemoto, and K. Semba

            "Experimentally realizable controlled NOT gate in a flux qubit/resonator system"

            Physical Review B 80 (22), 224509 (2009).

 

            ABSTRACT: We present an experimentally realizable microwave pulse sequence that effects a controlled-NOT (C-NOT) gate operation on a Josephson-junction-based flux qubit/resonator system with high-process fidelity. We obtained a C-NOT gate process fidelity of 0.988 (0.980) for a two-(three-)qubit/resonator system under ideal conditions and a fidelity of 0.903 for a two-qubit/resonator system under the best, currently achieved, experimental conditions. Our simulations show that this gate is a feasible first step toward multiqubit quantum-information processing with flux qubit/resonator systems.

 

70.    H. Sanada, T. Sogawa, H. Gotoh, Y. Tokura, H. Yamaguchi, H. Nakano, and H. Kamada

            "Magneto-optical spectroscopy of excitons and trions in charge-tunable quantum dots"

            Physical Review B 79 (12), 121303 (2009).

 

            ABSTRACT: We investigated the magneto-optical properties of charge-tunable GaAs quantum dots (QDs). Photoluminescence (PL) spectra change greatly with charge states of the QDs, and the PL lines of excited trions show complex magnetic field dependencies, which are quite different from that of the lowest radiative trion. A simulation using the configuration-interaction method supports the assignment of the PL emissions, and the effects of electron-electron and electron-hole interactions on shell and spin configurations of excited trions are discussed.

 

71.    S. Sasaki, H. Tamura, T. Akazaki, and T. Fujisawa

            "Fano-Kondo Interplay in a Side-Coupled Double Quantum Dot"

            Physical Review Letters 103 (26), 266806 (2009).

 

            ABSTRACT: We investigate low-temperature transport characteristics of a side-coupled double quantum dot where only one of the dots is directly connected to the leads. We observe Fano resonances, which arise from interference between discrete levels in one dot and the Kondo effect, or cotunneling in general, in the other dot, playing the role of a continuum. The Kondo resonance is partially suppressed by destructive Fano interference, reflecting novel Fano-Kondo competition. We also present a theoretical calculation based on the tight-binding model with the slave boson mean field approximation, which qualitatively reproduces the experimental findings.

 

72.    K. Semba, J. Johansson, K. Kakuyanagi, H. Nakano, S. Saito, H. Tanaka, and H. Takayanagi

            "Quantum state control, entanglement, and readout of the Josephson persistent-current qubit"

            Quantum Information Processing 8 (2-3)199-215 (2009).

 

            ABSTRACT: Quantum state control including entanglement, and readout of the Josephson persistent-current qubit, flux qubit, are reviewed. First, we mention our single-shot readout of quantum superposition state of a flux qubit by a current biased dc-SQUID. Second, we mention entangled state and vacuum Rabi oscillations of a flux-qubit LC-resonator system where qubit-resonator coupled state are controlled by a combination of microwave and DC-shift pulses, resulting in a controlling and measuring sequence analogous to atomic cavity QED. Third, we report our recent progress in high fidelity readout of a flux qubit state via Josephson bifurcation amplifier (JBA).

 

73.    H. Shibata, M. Asahi, T. Maruyama, T. Akazaki, H. Takesue, T. Honjo, and Y. Tokura

            "Optical Response and Fabrication of MgB2 Nanowire Detectors"

            Ieee Transactions On Applied Superconductivity 19 (3)358-360 (2009).

 

            ABSTRACT: We report the fabrication of MgB2 nanowire based on a liftoff-like technique and its optical response. A Si/C bilayer mask is formed as the negative pattern of the nanowire by e-beam lithography and the standard liftoff process. A 10 nm-thick MgB2 thin film is deposited on the pattern, which produces MgB2 nanowire with a width of down to 200 nm. We do not need to liftoff the Si/C bilayer because the MgB2 is well separated at the edge of the Si/C bilayer due to its overhang structure. The optical response at 1.5 mu m wavelength is measured at 4.2 K. For a 300 nm-wide nanowire, photoresponse signals with the repetition rate of 100 MHz are observed, and all signals disappear as the laser intensity decreases below 1.8 x 10(4) photon/pulse. On the other hand, the signals become intermittent as the laser intensity decreases for a 200 nm-wide nanowire. The signal disappears below 4 x 10(2). This shows that the nanowire works in the multi-photon detection regime.

 

74.    W. Shichi, T. Ito, M. Ichida, H. Gotoh, H. Kamada, and H. Ando

            "Dependence of Electron g-Factor on Barrier Aluminum Content in GaAs/AlGaAs Quantum Wells"

            Japanese Journal Of Applied Physics 48 (6), 063002 (2009).

 

            ABSTRACT: The effects of quantum confinement on electron g-factor tensor components, g(perpendicular to) and g(parallel to), were investigated for a wide variety of GaAs/AlxGa1-xAs quantum well structures, including the weak confinement regime, to determine the mapping of the g-factor components as functions of the aluminum content of an AlxGa1-xAs barrier and GaAs well thickness. The g-factor components were determined from the periods of electron spin precession, which were assessed by polarization- and time-resolved photoluminescence measurements under a magnetic field. The measured transverse component g(perpendicular to) was found to depend substantially on the barrier aluminum content, while the longitudinal component g(parallel to) was insensitive to the aluminum content. In addition to the experiments, the electron g-factor was analyzed theoretically on the basis of the three-band k.p perturbation theory by using Kiselev's method. Comparison of the experimental and theoretical results demonstrates that the three-band k.p calculation is sufficient to reproduce the main features of the experimental results including the effects of the barrier aluminum content. (C) 2009 The Japan Society of Applied Physics

 

75.    F. Shimizu, C. Hufnagel, and T. Mukai

            "Stable Neutral Atom Trap with a Thin Superconducting Disc"

            Physical Review Letters 103 (25), 253002 (2009).

 

            ABSTRACT: A stable magnetic quadrupole trap for neutral atoms on a superconducting Nb thin-film disc is demonstrated. The quadrupole field is composed of the magnetic field that is generated by vortices on the disc introduced by cooling the disc across the transition temperature with a finite field and an oppositely directed uniform field applied after cooling. The trap is stable when all trapping processes are performed above the dendritic instability temperature T-a. When the field intensity is changed below this temperature, the quadrupole field collapses and the trap disappears. The initial vortex density decreases even when the external field is changed at a temperature T > T-a. However, the vortex density is stabilized at an equilibrium density, whereas at T < T-a, it almost completely disappears. A stable trap can be formed, even when the initial vortices are introduced through a dendritic avalanche.

 

76.    K. Shimizu, K. Tamaki, and H. Fukasaka

            "Two-way protocols for quantum cryptography with a nonmaximally entangled qubit pair"

            Physical Review A 80 (2), 022323 (2009).

 

            ABSTRACT: This paper proposes a scheme for quantum cryptography with a nonmaximally entangled qubit pair. In a two-way configuration similar to quantum super dense coding, a two-bit key can be distributed by a round trip of one particle of the qubit pair and received by an appropriate joint measurement with the other. The security of our scheme is based on the quantum-mechanical impossibility of local unitary transformation between certain nonmaximally entangled states. Although an eavesdropper, Eve, can always identify the quantum state and intercept the key, it is impossible for her to resend the state with a unity probability and the legitimate parties inevitably detect her. Our protocol is also capable to quantum secure direct communication.

 

77.    K. Shimizu, and D. Hashimoto

            "Pairwise quantum correlation formed in an ensemble of atomic two-level systems storing squeezed light"

            Physical Review A 79 (6), 062312 (2009).

 

            ABSTRACT: This paper characterizes a quantum correlation formed in an ensemble of atomic two-level systems that stores a narrow-band squeezed state of light by coherently trapping an electron in an atomic superposed state a vertical bar 1 >>+b vertical bar 0 >>. In the storage process, a photonic quantum correlation in the squeezed light is transformed into an atomic quantum correlation between N atoms in an adiabatic way. If we regard the atomic superposed state as a 1/2-spin state and adopt the framework of a pairwise spin entanglement to analyze the atomic quantum correlation, we can identify a certain entangled state of a spin pair as the atomic signature of the squeezed light. The pairwise spin entangled state reflects all the physical properties of the squeezed light. By following the dissipative time evolution in the pairwise entangled state, we can describe the degraded properties of the squeezed light in retrieval.

 

78.    G. Shinkai, T. Hayashi, T. Ota, K. Muraki, and T. Fujisawa

            "Bidirectional Current Drag Induced by Two-Electron Cotunneling in Coupled Double Quantum Dots"

            Applied Physics Express 2 (8), 081101 (2009).

 

            ABSTRACT: We demonstrate a bidirectional current drag device, in which an electron tunneling through a double-quantum-clot (DQD) drags another electron in the other DQD in the same or opposite direction. The direction can be switched by choosing the corresponding cotunneling process of the two electrons. A reasonable drag effect is experimentally confirmed in a GaAs device. This result encourages optimizing the device for current mirror functions. (C) 2009 The Japan Society of Applied Physics

 

79.    G. Shinkai, T. Hayashi, T. Ota, and T. Fujisawa

            "Correlated Coherent Oscillations in Coupled Semiconductor Charge Qubits"

            Physical Review Letters 103 (5), 056802 (2009).

 

            ABSTRACT: We study coherent dynamics of two spatially separated electrons in a coupled semiconductor double quantum dot (DQD). Coherent oscillations in one DQD are strongly influenced by electronic states of the other DQD, or the two electrons simultaneously tunnel in a correlated manner. The observed coherent oscillations are interpreted as various two-qubit operations. The results encourage searching quantum entanglement in electronic devices.

 

80.    Y. Shinozaki, K. Sumitomo, M. Tsuda, S. Koizumi, K. Inoue, and K. Torimitsu

            "Direct Observation of ATP-Induced Conformational Changes in Single P2X(4) Receptors"

            Plos Biology 7 (5), e1000103 (2009).

 

            ABSTRACT: The ATP-gated P2X(4) receptor is a cation channel, which is important in various pathophysiological events. The architecture of the P2X(4) receptor in the activated state and how to change its structure in response to ATP binding are not fully understood. Here, we analyze the architecture and ATP-induced structural changes in P2X(4) receptors using fast-scanning atomic force microscopy (AFM). AFM images of the membrane-dissociated and membrane-inserted forms of P2X(4) receptors and a functional analysis revealed that P2X(4) receptors have an upward orientation on mica but lean to one side. Time-lapse imaging of the ATP-induced structural changes in P2X(4) receptors revealed two different forms of activated structures under 0 Ca2+ conditions, namely a trimer structure and a pore dilation-like tripartite structure. A dye uptake measurement demonstrated that ATP-activated P2X(4) receptors display pore dilation in the absence of Ca2+. With Ca2+, the P2X(4) receptors exhibited only a disengaged trimer and no dye uptake was observed. Thus our data provide a new insight into ATP-induced structural changes in P2X(4) receptors that correlate with pore dynamics.

 

81.    V. K. Singh, K. Yamazaki, T. Tawara, H. Okamoto, and H. Yamaguchi

            "Fabrication of Nanomechanical Structures from Bulk-GaAs Using Angled Ion Etching"

            Applied Physics Express 2 (6), 065001 (2009).

 

            ABSTRACT: We demonstrate a novel fabrication technique for making nanomechanical structures from bulk materials with no sacrificial layer. Angled ion etching is used to suspend single- and double-clamped beams from GaAs initially. Both beams are fabricated successfully by dry anisotropic ion etching. Resonance characteristics of the fabricated beams are also investigated from 300 to 15 K. A quality factor Q of 5700 is obtained at 40 K, showing a high mechanical reliability. This technique does not rely on conventional sacrificial etching and will enable us to fabricate electro-mechanical structures from a large number of bulk materials in the micro/nano electro mechanical systems (MEMS/NEMS) field. (c) 2009 The Japan Society of Applied Physics

 

82.    T. Sogawa, H. Sanada, H. Gotoh, H. Yamaguchi, S. Miyashita, and P. V. Santos

            "Spatial and temporal modulation of exciton photoluminescence properties in GaAs/AlAs dynamic quantum dots formed by surface acoustic waves"

            Physical Review B 80 (7), 075304 (2009).

 

            ABSTRACT: We report on the dynamic optical properties of excitons in moving dots (dynamic quantum dots, DQDs) formed by the interference of orthogonally propagating surface acoustic waves (SAWs) in GaAs/AlAs quantum wells. Spatially and time-resolved photoluminescence (PL) measurements using a synchronized excitation method clearly demonstrate the formation of two interpenetrating square arrays of DQDs, one consisting of potential dynamic dots (p-DDs) formed by the SAW piezoelectric potential and the other consisting of strain dynamic dots created by the strain-induced band-gap modulation. We found that the p-DDs induce a PL-polarization anisotropy, leading to a checkered spatial modulation pattern for the preferential PL-polarization direction. Carrier dynamics under SAW fields, which affect the effective diffusion length of excitons and the PL quenching time, is invoked to clarify the physical mechanisms underlying the PL-mapping spectra obtained by the synchronized excitation method. A theoretical analysis on the band structures and optical transition properties modified by SAWs consistently explains the experimental results.

 

83.    T. Sogawa, H. Sanada, H. Gotoh, H. Yamaguchi, S. Miyashita, and P. V. Santos

            "Photoluminescence dynamics in GaAs/AlAs quantum wells modulated by one-dimensional standing surface acoustic waves"

            Applied Physics Letters 94 (13), 131912 (2009).

 

            ABSTRACT: The effects of standing surface acoustic waves (SAWs) on carrier dynamics in GaAs/AlAs quantum wells are investigated by spatially and time-resolved photoluminescence (PL) spectroscopy. We found that the PL spectra vary considerably depending on the position and the phase of the standing SAW field. The PL spectra are characterized by oscillations in the PL intensity and emission energy due to the motion of free carriers and excitons driven by the piezoelectric fields as well as by the strain-induced band-gap gradient. It is also demonstrated that the positions of the nodes and antinodes of the standing SAW are precisely controlled.

 

84.    K. Sumitomo, Y. Shinozaki, D. Takagi, H. Nakashima, Y. Kobayashi, and K. Torimitsu

            "Atomic Force Microscopy Observation of Membrane Proteins Suspended over Carbon Nanotube Network"

            Japanese Journal Of Applied Physics 48 (8), 08JB18 (2009).

 

            ABSTRACT: Atomic force microscopy (AFM) imaging of membrane proteins suspended over a nanostructure in liquid is a promising way to understand the structure and function of working proteins, although the membrane deformation that occurs during scanning makes it difficult to obtain a high resolution image. This study proposes an artificial cell system for the AFM observation of functional membrane proteins that consists of a sub-micron well on Si, a biological membrane, and a carbon nanotube (CNT) network. We successfully observed molecular-scale images of a purple membrane suspended over sub-micron well patterns. By using a CNT network to hold the suspended membrane, we suppressed the membrane deformation caused by the "imaging force". The CNT network takes the place of a cytoskeleton in supporting the cell membrane suspended over the well thus improving the spatial resolution of AFM measurement. (C) 2009 The Japan Society of Applied Physics

 

85.    I. Sychugov, H. Omi, T. Murashita, and Y. Kobayashi

            "Optical and electrical characterization at the nanoscale with a transparent probe of a scanning tunnelling microscope"

            Nanotechnology 20 (14), 145706 (2009).

 

            ABSTRACT: A new type of scanning probe microscope, combining features of the scanning tunnelling microscope, the scanning tunnelling luminescence microscope with a transparent probe and the aperture scanning near-field optical microscope, is described. Proof-of-concept experiments were performed under ultrahigh vacuum conditions at varying temperature on GaAs/AlAs heterostructures.

 

86.    D. Takagi, Y. Kobayashi, and Y. Hommam

            "Carbon Nanotube Growth from Diamond"

            Journal Of The American Chemical Society 131 (20)6922-+ (2009).

 

            ABSTRACT: We demonstrate that nanosize diamond particles in a stable solid phase can act as nuclei for carbon nanotube (CNT) growth by chemical vapor deposition. This growth process is explained by a new growth mechanism, where the surface diffusion of carbon adatoms on the solid surface of nanoparticles plays an important role, contrary to the bulk diffusion in conventional metal catalysts. The use of diamond nanoparticles overcomes the issues of deactivation due to fusion with each other or reaction with substrate materials in the CNT growth using conventional metal catalysts and promotes high-density CNT growth from highly dense nanoparticles on any substrate.

 

87.    H. Takahashi, K. Kato, H. Nakano, M. Kitajima, K. Ohmori, and K. G. Nakamura

            "Optical control and mode selective excitation of coherent phonons in YBa2Cu3O7-delta"

            Solid State Communications 149 (43-44)1955-1957 (2009).

 

            ABSTRACT: Femtosecond time-resolved reflectivity measurement is performed on YBa2Cu3O7-delta films. Coherent phonons of both the Ba-O and Cu-O modes are observed at frequencies of 3.4 and 4.3 THz, respectively. Amplitudes of both Ba-O and Cu-O modes are optically manipulated by using a pair of femtosecond pulses, the separation time of which is controlled. Coherent phonons of the Ba-O and Cu-O modes are completely suppressed at the double-pulse separation times of 135.0 and 108.5 fs and those amplitudes are enhanced at 270 and 217 fs, respectively. (C) 2009 Elsevier Ltd. All rights reserved.

 

88.    K. Takashina, Y. Niida, V. T. Renard, A. Fujiwara, T. Fujisawa, and Y. Hirayama

            "NEGATIVE MAGNETORESISTANCE OF A SILICON 2DEG UNDER IN-PLANE MAGNETIC FIELD DUE TO SPIN-SPLITTING OF UPPER SUBBANDS"

            International Journal Of Modern Physics B 23 (12-13)2938-2942 (2009).

 

            ABSTRACT: We examine the effect of an in-plane magnetic field on the resistance of a 2-dimensional electron system confined in a silicon quantum well when the Fermi energy is tuned through the upper valley-subband edge while the electrons are otherwise valley-polarized. In contrast to previous experiments on valley-degenerate systems which only showed positive magnetoresistance, when the Fermi energy is at or near the upper valley-subband edge, the magnetoresistance is found to show a distinct negative contribution which is interpreted as being due to spin polarization of the upper valley-subband.

 

89.    K. Takashina, K. Nishiguchi, Y. Ono, A. Fujiwara, T. Fujisawa, Y. Hirayama, and K. Muraki

            "Electrons and holes in a 40 nm thick silicon slab at cryogenic temperatures"

            Applied Physics Letters 94 (14), 142104 (2009).

 

            ABSTRACT: We demonstrate low temperature operation of an electron-hole bilayer device based on a 40 nm thick layer of silicon in which electrons and holes can be simultaneously induced and contacted independently. The device allows the application of bias between the electrons and holes enhancing controllability over density and confining potential. We confirm that drag measurements are possible with the structure.

 

90.    H. Takesue, and B. Miquel

            "Entanglement swapping using telecom-band photons generated in fibers"

            Optics Express 17 (13)10748-10756 (2009).

 

            ABSTRACT: We report the first entanglement swapping experiment using entangled photon-pair sources based on spontaneous four-wave mixing (SFWM). The 1.5-mu m band entangled photon pairs generated by SFWM in two independent 500-m dispersion shifted fibers exhibited quantum interference, thanks to the negligible walk-off between the pump and photon pairs. The use of 500-MHz gated-mode InGaAs/InP avalanche photodiodes based on the sine-wave gating technique increased the fourfold coincidence rate. As a result, the formation of an entanglement between photons from independent sources was successfully observed. (C) 2009 Optical Society of America

 

91.    H. Takesue, and Y. Noguchi

            "Implementation of quantum state tomography for time-bin entangled photon pairs"

            Optics Express 17 (13)10976-10989 (2009).

 

            ABSTRACT: Quantum state tomography (QST) is an important method for evaluating the quality of entangled photon pairs, and has been widely used to measure polarization entanglement. However, QST has not been applied to time-bin entanglement, which is a type of entanglement suitable for fiber transmission. In this paper, we clarify the way to implement QST on time-bin entangled photon pairs using a 1-bit delayed interferometer. We also provide experimental results for a demonstration of QST for time-bin entangled photon pairs generated using spontaneous four-wave mixing in a dispersion shifted fiber. (C) 2009 Optical Society of America

 

92.    K. Tamaki, N. Lutkenhaus, M. Koashi, and J. Batuwantudawe

            "Unconditional security of the Bennett 1992 quantum-key-distribution scheme with a strong reference pulse"

            Physical Review A 80 (3), 032302 (2009).

 

            ABSTRACT: We prove the unconditional security of the original Bennett 1992 protocol with strong reference pulse. We show that we may place a projection onto suitably defined qubit spaces before the receiver, which makes the analysis as simple as qubit-based protocols. Unlike the single-photon-based qubits, the qubits identified in this scheme are almost surely detected by the receiver even after a lossy channel. This leads to the key generation rate that is proportional to the channel transmission rate for proper choices of experimental parameters.

 

93.    K. Tamaru, K. Nonaka, M. Nagase, H. Yamaguchi, S. Warisawa, and S. Ishihara

            "Direct Actuation of GaAs Membrane with the Microprobe of Scanning Probe Microscopy"

            Japanese Journal Of Applied Physics 48 (6), 06FG06 (2009).

 

            ABSTRACT: A method for evaluating the dynamic characteristics of micro- and nanoresonators with high spatial resolution is proposed. The mechanical resonance of circular micromembrane resonators is directly induced by voltage applied from the microprobe of a scanning probe microscopy (SPM) system. The vibration amplitude is simultaneously detected as height information by SPM. Experimentally, the resonant properties of fundamental and higher-order modes of 200-nm-thick GaAs micromembranes were measured. The frequency of the highest mode is 3.4 MHz and its resonant amplitude is about 1 nm. The resonant amplitude increases with increasing actuation voltage in a linear manner at voltages below 180 mV. Large actuation voltage induces nonlinear vibration with the spring soften effect, which originates from the strong attractive force induced by the electronic field between the probe and membrane. The high tapping force, which is repulsive, induces another type of nonlinear vibration caused by the spring harden effect. The simultaneous actuation and detection for mechanical resonators based on SPM technology reveals the characteristics of the mechanical interaction force between the micromembrane and microprobe. (C) 2009 The Japan Society of Applied Physics

 

94.    T. Tanabe, K. Nishiguchi, E. Kuramochi, and M. Notomi

            "Low power and fast electro-optic silicon modulator with lateral p-i-n embedded photonic crystal nanocavity"

            Optics Express 17 (25)22505-22513 (2009).

 

            ABSTRACT: We have fabricated high-Q photonic crystal nanocavities with a lateral p-i-n structure to demonstrate low-power and high-speed electro-optic modulation in a silicon chip. GHz operation is demonstrated at a very low (mu W level) operating power, which is about 4.6 times lower than that reported for other cavities in silicon. This low-power operation is due to the small size and high-Q of the photonic crystal nanocavity. (C) 2009 Optical Society of America

 

95.    T. Tanabe, M. Notomi, H. Taniyama, and E. Kuramochi

            "Dynamic Release of Trapped Light from an Ultrahigh-Q Nanocavity via Adiabatic Frequency Tuning"

            Physical Review Letters 102 (4), 043907 (2009).

 

            ABSTRACT: Adiabatic frequency shifting is demonstrated by tuning an ultrahigh-Q photonic crystal nanocavity dynamically. By resolving the output temporally and spectrally, we showed that the frequency of the light in the cavity follows the cavity resonance shift and remains in a single mode throughout the process. This confirmed unambiguously that the frequency shift results from the adiabatic tuning. We have employed this process to achieve the dynamic release of a trapped light from an ultrahigh-Q cavity and thus generate a short pulse. This approach provides a simple way of tuning Q dynamically.

 

96.    Y. Taniyasu, and M. Kasu

            "MOVPE growth of single-crystal hexagonal AlN on cubic diamond"

            Journal Of Crystal Growth 311 (10)2825-2830 (2009).

 

            ABSTRACT: We have obtained single-crystal aluminum nitride (AlN) layers on diamond (1 1 1) substrates by metalorganic vapor-phase epitaxy (MOVPE). When the thermal cleaning temperature of the substrate and growth temperature of the AlN layer were below 1100 degrees C, the AlN layer had multi-domain structures mainly consisting of rotated domains. An interface layer, consisting of amorphous carbon and poly-crystal AlN, was formed between the AlN layer and the diamond substrate. On the other hand, when the thermal cleaning temperature and growth temperature were above 1200 degrees C, a single-crystal AlN layer was grown and no interface layer was formed. Therefore, we attribute the multi-domain structures to the interface layer. Even at the growth temperature of 1100 degrees C, by performing the thermal cleaning at 1200 degrees C, the single-crystal AlN layer was obtained, indicating that the thermal cleaning temperature of the substrate is a critical factor for the formation of the interface layer. The epitaxial relationship between the single-crystal AlN layer and the diamond (1 1 1) substrate was determined to be [0 0 0 1](AlN) || [1 1 1](diamond) and [1 0 (1) over bar 0](AlN) || [1 (1) over bar 0](diamond). The AlN surface had Al polarity and no inversion domains were observed in the AlN layer. (C) 2009 Elsevier B.V. All rights reserved.

 

97.    T. Tawara, H. Kamada, S. Hughes, H. Okamoto, M. Notomi, and T. Sogawa

            "Cavity mode emission in weakly coupled quantum dot - cavity systems"

            Optics Express 17 (8)6643-6654 (2009).

 

            ABSTRACT: We study the origin of bright leaky-cavity mode emission and its influence on photon statistics in weakly coupled quantum dot semiconductor cavity systems, which consist of a planar photonic-crystal and several quantum dots. We present experimental measurements that show that when the system is excited above the barrier energy, then bright cavity mode emissions with nonzero detuning are dominated by radiative recombinations of deep-level defects in the barrier layers. Under this excitation condition, the second-order photon autocorrelation measurements reveal that the cavity mode emission at nonzero detuning exhibits classical photon-statistics, while the bare exciton emission shows a clear partial anti-bunching. As we enter a Purcell factor enhancement regime, signaling a clear cavity-exciton coupling, the relative weight of the background recombination contribution to the cavity emission decreases. Consequently, the anti-bunching behavior is more significant than the bare exciton case - indicating that the photon statistics becomes more non-classical. These measurements are qualitatively explained using a medium-dependent master equation model that accounts for several excitons and a leaky cavity mode. (c) 2009 Optical Society of America

 

98.    Y. Tokura, T. Obata, T. Hatano, and S. Tarucha

            "Electron-Spin Manipulation in Quantum Dot Systems"

            Electron Spin Resonance And Related Phenomena In Low-dimensional 11515-34 (2009).

 

            ABSTRACT: Recent experimental and theoretical progress as regards the full manipulation of electron spins in quantum dot systems is reviewed. In order to realize coherent single-spin manipulation, we propose quantum-dot devices with an integrated high-frequency line designed to generate an ac magnetic field. We also discuss in detail the electric dipole spin resonance realized with a slanting Zeeman field. After discussions of the exchange coupling between the two electron spins in a double quantum-dot system, we present current spectra of a hybrid vertical-lateral double quantum-dot device.

 

99.    Y. Tokura, K. Ono, and S. Tarucha

            "Tunneling current through g-factor engineered series quantum dots"

            Physica Status Solidi B-basic Solid State Physics 246 (4)740-743 (2009).

 

            ABSTRACT: We evaluate resonant tunneling current via series quantum dots with different g-factors by Bloch equation method. We found that the resonant current is always singly peaked as a function of bias and its peak position depends on the gate voltage. When the rate of spontaneous phonon emission is very small, the shift of the peak positions between single spin transport and both spin transport corresponds to the half of the difference of the Zeemann energy. In contrast, when the phonon assisted tunneling predominates, the peak always appears at one of the resonant tunneling conditions for larger bias. These features are explained by spin blockade effect. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

 

100.    Y. Tokura

            "Electric spin orchestra"

            Nature Physics 5 (1)12-13 (2009).

 

            ABSTRACT:

 

101.    C. L. Tsai, Y. Kobayashi, T. Akasaka, and M. Kasu

            "Molecular beam epitaxial growth of hexagonal boron nitride on Ni(111) substrate"

            Journal Of Crystal Growth 311 (10)3054-3057 (2009).

 

            ABSTRACT: We demonstrate hexagonal boron nitride (h-BN) epitaxial growth on Ni(111) substrate by molecular beam epitaxy (MBE) at 890 degrees C. Elemental boron evaporated by an electron-beam gun and active nitrogen generated by a radio-frequency (RF) plasma source were used as the group-III and -V sources, respectively. Reflection high-energy electron diffraction revealed a streaky (1 x 1) pattern, indicative of an atomically flat surface in the ongoing growth. Correspondingly, atomic force microscopy images exhibit atomically smooth surface of the resulting h-BN film. X-ray diffraction characterization confirmed the crystallinity of the epitaxial film to be h-BN, and its X-ray rocking curve has a full-width at half-maximum of 0.61 degrees, which is the narrowest ever reported for h-BN thin film. The epitaxial alignments between the h-BN film and the Ni substrate were determined to be [0001](h-BN)parallel to[111](Ni), [11 (2) over bar0](h-BN)parallel to[(1) over bar 10](Ni), and [(1) over bar 100](h-BN)parallel to[(1) over bar(1) over bar2](Ni). (C) Elsevier B.V. All rights reserved.

 

102.    K. Ueda, and M. Kasu

            "Beryllium-doped single-crystal diamond grown by microwave plasma CVD"

            Diamond And Related Materials 18 (2-3)121-123 (2009).

 

            ABSTRACT: We performed beryllium (Be) doping to diamond by inserting a solid Be-rod into the plasma ball during microwave plasma CVD growth. The Be concentration can be controlled in the range from similar to 10(16) to similar to 10(18) cm(-3) by changing the Be-rod insertion depth in the plasma ball and the microwave power. In cathodoluminescence (CL) spectra of Be-doped CVD films, we observed a peak at 4.760 eV and its phonon replica as well as free-exciton (FE)related emissions. Peak energies of these emissions are close to those of Be-related emissions from Be-implanted diamond films. (C) 2008 Elsevier B.V. All rights reserved.

 

103.    Y. Ueno, Y. Toda, S. Adachi, R. Morita, and T. Tawara

            "Coherent transfer of orbital angular momentum to excitons by optical four-wave mixing"

            Optics Express 17 (22)20567-20574 (2009).

 

            ABSTRACT: We demonstrate the coherent transfer of optical orbital angular momentum (OAM) to the center of mass momentum of excitons in semiconductor GaN using a four-wave mixing (FWM) process. When we apply the optical vortex (OV) as an excitation pulse, the diffracted FWM signal exhibits phase singularities that satisfy the OAM conservation law, which remain clear within the exciton dephasing time (similar to 1ps). We also demonstrate the arbitrary control of the topological charge in the output signal by changing the OAM of the input pulse. The results provide a way of controlling the optical OAM through carriers in solids. Moreover, the time evolution of the FWM with OAM leads to the study of the closed-loop carrier coherence in materials. (C) 2009 Optical Society of America

 

104.    Y. D. Wang, Y. Li, F. Xue, C. Bruder, and K. Semba

            "Cooling a micromechanical resonator by quantum back-action from a noisy qubit"

            Physical Review B 80 (14), 144508 (2009).

 

            ABSTRACT: We study the role of qubit dephasing in cooling a mechanical resonator by quantum back-action. With a superconducting flux qubit as a specific example, we show that ground-state cooling of a mechanical resonator can only be realized if the qubit dephasing rate is sufficiently low.

 

105.    Y. D. Wang, A. Kemp, and K. Semba

            "Coupling superconducting flux qubits at optimal point via dynamic decoupling with the quantum bus"

            Physical Review B 79 (2), 024502 (2009).

 

            ABSTRACT: We propose a scheme with dc control of finite bandwidth to implement a two-qubit gate for superconducting flux qubits at the optimal point. We provide a detailed nonperturbative analysis on the dynamic evolution of the qubits interacting with a common quantum bus. An effective qubit-qubit coupling is induced while decoupling the quantum bus with proposed pulse sequences. The two-qubit gate is insensitive to the initial state of the quantum bus and applicable to nonperturbative coupling regime which enables rapid two-qubit operation. This scheme can be scaled up to multiqubit coupling.

 

106.    Z. Z. Wang, D. M. Chen, T. Ota, and T. Fujisawa

            "Time-Dependent Local Potential Induced by Scanning Gate Microscopy"

            Japanese Journal Of Applied Physics 48 (4), 04C148 (2009).

 

            ABSTRACT: We have developed a new high-frequency scanning gate microscopy (HF-SGM), in which high-frequency electrical signals can be applied on the conductive tip of an atomic force microscope (AFM). The high-frequency characteristics are investigated by correlation measurement on a semiconductor quantum point contact (QPC). The time-dependent potential of the tunneling barrier is induced from the AFM tip and probed with another voltage pulse applied on the source electrode. The measurement indicates that an electrical pulse as short as 5 ns can be applied without significant distortion. The demonstrated HF-SGM would allow us to investigate the dynamic response from various nanostructures. (C) 2009 The Japan Society of Applied Physics

 

107.    K. Wen, K. Tamaki, and Y. Yamamoto

            "Unconditional Security of Single-Photon Differential Phase Shift Quantum Key Distribution"

            Physical Review Letters 103 (17), 170503 (2009).

 

            ABSTRACT: In this Letter, we prove the unconditional security of the single-photon differential phase shift quantum key distribution (DPS-QKD) protocol, based on the conversion to an equivalent entanglement-based protocol. We estimate the upper bound of the phase error rate from the bit error rate, and show that the DPS-QKD protocol can generate an unconditionally secure key when the bit error rate is not greater than 4.12%. This proof is the first step to the unconditional security proof of a coherent state DPS-QKD.

 

108.    S. Yamada, H. Yamaguchi, and S. Ishihara

            "Focus on Novel Nanoelectromechanical 3D Structures: Fabrication and Properties FOREWORD"

            Science And Technology Of Advanced Materials 10 (3), 030301 (2009).

 

            ABSTRACT:

 

109.    A. Yamamoto, M. Yamashita, and N. Kawakami

            "Nonadiabatic Dynamics of Ultracold Fermions in Optical Superlattices"

            Journal Of The Physical Society Of Japan 78 (12), 123002 (2009).

 

            ABSTRACT: We study the time-dependent dynamical properties of two-component ultracold fermions in a one-dimensional optical superlattice by applying the adaptive time-dependent density matrix renormalization group to a repulsive Hubbard model with an alternating superlattice potential. We clarify how the time evolution of local quantities Occurs when the superlattice potential is suddenly changed to a normal one. For a Mott-type insulating state at quarter filling, the time evolution exhibits a profile similar to that expected for bosonic atoms, where correlation effects are less important. On the other hand, for a band-type insulating state at half filling, the strong repulsive interaction induces an unusual pairing of fermions, resulting in some striking properties in time evolution, such as a paired fermion co-tunneling process and the suppression of local spin moments. We further address the effect of a confining potential, which causes spatial confinement of the paired fermions.

 

110.    A. Yamamoto, M. Yamashita, and N. Kawakami

            "Trapped Ultracold Fermions in Double-Well Optical Lattices"

            Journal Of The Physical Society Of Japan 78 (12), 124001 (2009).

 

            ABSTRACT: We study the ground state properties of ultracold Fermions trapped in a one-dimensional double-well optical lattice by using the density-matrix renormalization group method. The system is described by an extended Hubbard model with alternating hopping integrals and an external harmonic confining potential. We clarify the characteristic features of the metal-insulator phase transition originating from the double-well structure of the lattices. Several different types of insulating regions coexist when the number of atoms at each site is an integer or a half integer. We found that each insulating phase except for a band insulator exhibits rather large local density fluctuations, reflecting the strong dimerization of atoms within the unit cells of double-well lattices. The phase characteristics are elucidated in detail by investigating the profiles of the local density of atoms, the local density (spin) fluctuations, the double-occupancy probability and the spatially extended sp in correlations.

 

111.    M. Yamashita, and M. W. Jack

            "Mott-insulator shells in the three-dimensional Bose-Hubbard model with harmonic confinement"

            Physical Review A 79 (2), 023609 (2009).

 

            ABSTRACT: Ultracold atom experiments offer unprecedented potential for the quantitative comparison of quantum many-body effects with theory. This comparison is hindered by the lack of numerical methods capable of dealing with these large inhomogeneous three-dimensional systems. In this paper we demonstrate the applicability of a highly efficient numerical method based on the Gutzwiller approximation for calculating the ground state of the Bose-Hubbard model in the regimes of the recent cold atom experiments. The numerical method is applied to the experimental regime employed by Campbell [Science 314, 281 (2006)], where Mott-insulator shells were directly imaged via atomic clock shifts. We calculate several quantities that are closely related to the current experimental measurement methods: average number distributions, momentum distributions, two-photon spectra, and three-body recombination loss rates. Our results shed light on a number of features of the experimental observations and clarify both the crossover behavior around the superfluid-Mott-insulator transition point and the experimentally observed three-body decay rate of the Mott-insulator shells.

 

112.    G. Q. Zhang, K. Tateno, H. Sanada, T. Tawara, H. Gotoh, and H. Nakano

            "Synthesis of GaAs nanowires with very small diameters and their optical properties with the radial quantum-confinement effect"

            Applied Physics Letters 95 (12), 123104 (2009).

 

            ABSTRACT: grew the GaAs nanowires by using size-selective gold particles with nominal diameters of 5, 10, 20, 40, and 60 nm. The diameter-controlled nanowires enable us to observe blueshifts of the free exitononic emission peak from individual nanowires with decreasing gold-particle size due to the two-dimensional radial quantum-confinement effect. We also analyze the absorption and emission polarization anisotropies of these bare GaAs quantum nanowires. (C) 2009 American Institute of Physics. [doi:10.1063/1.3229886]

 

113.    Q. Zhang, H. Takesue, T. Honjo, K. Wen, T. Hirohata, M. Suyama, Y. Takiguchi, H. Kamada, Y. Tokura, O. Tadanaga, Y. Nishida, M. Asobe, and Y. Yamamoto

            "Megabits secure key rate quantum key distribution"

            New Journal Of Physics 11, 045010 (2009).

 

            ABSTRACT: Quantum cryptography can provide unconditional secure communication between two authorized parties based on the basic principles of quantum mechanics. However, imperfect practical conditions limit its transmission distance and communication speed. Here, we implemented the differential phase shift (DPS) quantum key distribution (QKD) with an up-conversion-assisted hybrid photon detector (HPD) and achieved a 1.3 Mbits per second secure key rate over a 10 km fiber, which is tolerant against photon number splitting (PNS) attack, general collective attacks on individual photons and any other known sequential unambiguous state discrimination (USD) attacks.