Two-dimensional system

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>>Quantum dots/Charge qubit >>Two-dimensional system >>Low-temperature nanoprobe Two-Dimensional System We investigate many-body effects in two-dimensional systems, particularly in quantum Hall systems, formed in GaAs/AlGaAs or Si/SiO2 heterostructures and in graphene by transport or nuclear spin measurements. Figure: Spin polarization in a high-mobility GaAs/AlGaAs QH system detected by NMR [Science 335, 828 (2012)]. Selected publications GaAs/AlGaAs quantum Hall system Unraveling the Spin Polarization of the nu = 5/2 Fractional Quantum Hall State L. Tiemann, G. Gamez, N. Kumada, and K. Muraki Science 335, 828 (2012). Low-Frequency Spin Fluctuations in Skyrmions Confined by Wires: Measurements of Local Nuclear Spin Relaxation Takashi Kobayashi, Norio Kumada, Takeshi Ota, Satoshi Sasaki, and Yoshiro Hirayama Phys. Rev. Lett. 107, 126807 (2011). Intrinsic Gap and Exciton Condensation in the nu_T=1 Bilayer System P. Giudici, K. Muraki, N. Kumada, and T. Fujisawa Phys. Rev. Lett. 104, 056802 (2010). Spin-dependent phase diagram of the nu_T=1 bilayer electron system P. Giudici, K. Muraki, N. Kumada, Y. Hirayama, and T. Fujisawa Phys. Rev. Lett. 100, 106803 (2008). Modulation of bilayer quantum Hall states by tilted-field-induced subband-Landau-level coupling N. Kumada, K. Iwata, K. Tagashira, Y. Shimoda, K. Muraki, Y. Hirayama, and A. Sawada Phys. Rev. B. 77, 155324 (2008). NMR Evidence for Spin Canting in a Bilayer nu = 2 Quantum Hall System N. Kumada, K. Muraki, and Y. Hirayama Phys. Rev. Lett. 99, 076805 (2007). Low-Frequency Spin Dynamics in a Canted Antiferromagnet N. Kumada, K. Muraki, and Y. Hirayama Science 313, 329 (2006.) Spin Degree of Freedom in the nu = 1 Bilayer Electron System Investigated by Nuclear Spin Relaxation N. Kumada, K. Muraki, K. Hashimoto, and Y. Hirayama Phys. Rev. Lett. 94, 096802 (2005). Coulomb drag as a probe of the nature of compressible states in a magnetic field K. Muraki, J. G. S. Lok, S. Kraus, W. Dietsche, K. von Klitzing, D. Schuh, M. Bichler, and W. Wegscheider Phys. Rev. Lett. 92, 246801 (2004). Phase diagram of interacting composite fermions in the bilayer nu=2/3 quantum Hall effect N. Kumada, D. Terasawa, Y. Shimoda, H. Azuhata, A. Sawada, Z. F. Ezawa, K. Muraki, T. Saku, and Y. Hirayama Phys. Rev. Lett. 89, 116802 (2002). Charge excitations in easy-axis and easy-plane quantum Hall ferromagnets K. Muraki, T. Saku, and Y. Hirayama Phys. Rev. Lett. 87, 196801 (2001). Electron-nuclear spin interactions Electric Field Induced Nuclear Spin Resonance Mediated by Oscillating Electron Spin Domains in GaAs-Based Semiconductors N. Kumada, T. Kamada, S. Miyashita, Y. Hirayama, and T. Fujisawa Phys. Rev. Lett. 101, 137602 (2008). Decoherence of nuclear spins due to dipole-dipole interactions probed by resistively detected nuclear magnetic resonance T. Ota, G. Yusa, N. Kumada, S. Miyashita, T. Fujisawa, and Y. Hirayama Appl. Phys. Lett. 91, 193101 (2007). Nuclear spin population and its control toward initialization using an all-electrical submicron scale nuclear magnetic resonance device T. Ota, G. Yusa, N. Kumada, S. Miyashita, and Y. Hirayama Appl. Phys. Lett. 90, 102118 (2007). Controlled multiple quantum coherences of nuclear spins in a nanometre-scale device G. Yusa, K. Muraki, K. Takashina, K. Hashimoto, and Y. Hirayama Nature 434, 1001 (2005). Effects of inversion asymmetry on electron-nuclear spin coupling in semiconductor heterostructures: Possible role of spin-orbit interactions K. Hashimoto, K. Muraki, N. Kumada, T. Saku, and Y. Hirayama Phys. Rev. Lett. 94, 146601 (2005). Electrically controlled nuclear spin polarization and relaxation by quantum-Hall states K. Hashimoto, K. Muraki, T. Saku, and Y. Hirayama Phys. Rev. Lett. 88, 176601 (2002). Edge magnetoplasmon measurement Edge magnetoplasmon transport in gated and ungated quantum Hall systems N. Kumada, H. Kamata, and T. Fujisawa Phys. Rev. B 84, 045314 (2011). Voltage-controlled group velocity of edge magnetoplasmon in the quantum Hall regime H. Kamata, T. Ota, K. Muraki, and T. Fujisawa Phys. Rev. B 81, 085329 (2010). Si/SiO2 heterostructures Impact of Valley Polarization on the Resistivity in Two Dimensions K. Takashina, Y. Niida, V. T. Renard, A. Fujiwara, T. Fujisawa, K. Muraki, and Y. Hirayama Phys. Rev. Lett. 106, 196403 (2011). Electrons and holes in a 40 nm thick silicon slab at cryogenic temperatures K. Takashina, K. Nishiguchi, Y. Ono, A. Fujiwara, T. Fujisawa, Y. Hirayama, and K. Muraki Appl. Phys. Lett. 94, 142104 (2009). Spin splitting of upper electron subbands in a SiO2/Si(100)/SiO2 quantum well with in-plane magnetic field Y. Niida, K. Takashina, A. Fujiwara, T. Fujisawa, and Y. Hirayama Appl. Phys. Lett. 94, 142101 (2009). Anomalous Resistance Ridges along Filling Factor nu=4i K. Takashina, M. Brun, T. Ota, D. K. Maude, A. Fujiwara, Y. Ono, Y. Takahashi, and Y. Hirayama Phys. Rev. Lett. 99, 036803 (2007). Valley polarization in Si(100) at zero magnetic field K. Takashina, Y. Ono, A. Fujiwara, Y. Takahashi, and Y. Hirayama Phys. Rev. Lett. 96, 236801 (2006). Valley splitting control in SiO2/Si/SiO2 quantum wells in the quantum Hall regime K. Takashina, A. Fujiwara, S. Horiguchi, Y. Takahashi, and Y. Hirayama Phys. Rev. B 69, 161304(R) (2004). Other topics Boundary-Mediated Electron-Electron Interactions in Quantum Point Contacts V. T. Renard, O. A. Tkachenko, V. A. Tkachenko, T. Ota, N. Kumada, J.-C. Portal, and Y. Hirayama Phys. Rev. Lett. 100, 186801 (2008). Landau-level Hybridization and the Quantum Hall Effect in InAs/(AlSb)/GaSb Electron-Hole System K. Suzuki, K. Takashina, S. Miyashita, and Y. Hirayama Phys. Rev. Lett. 93, 016803 (2004).

3-1 Morinosato-Wakamiya, Atugi, Kanagawa 243-0198, Japan Qauntum Solid State Physics Research Group Physical Science Labortory NTT Basic Research Laboratories NTT