Research topics
>>Japanese
I am interested in many-body physics in two-dimensional electron systems (2DESs). In particular, I investigate electron spin states in a quantum Hall system by resistively-detected nuclear magnetic resonance. Recently, I started research on plasmon transport in GaAs/AlGaAs 2DESs or graphene using time-resolved transport measurement.


  • Plasmon transport in graphene and GaAs/AlGaAs 2DESs

  • Quantum Hall effect

  • Bilayer quantum Hall state at nu=1

  • Bilayer quantum Hall state at nu=2

  • Bilayer quantum Hall state at nu=2/3

  • Control of nuclear spins in semiconductors
    clear
    • Electric Field Induced Nuclear Spin Resonance Mediated by Oscillating Electron Spin Domains in GaAs-Based Semiconductors
      N. Kumada, T. Kamada, S. Miyashita, Y. Hirayama, T. Fujisawa
      Phys. Rev. Lett. 101, 137602 (2008).
    Abstract--
    We demonstrate an alternative nuclear spin resonance using radio frequency (RF) electric field (nuclear electric resonance: NER) instead of magnetic field. The NER is based on the electronic control of electron spins forming a domain structure. The RF electric field applied to a gate excites spatial oscillations of the domain walls and thus temporal oscillations of the hyperfine field to nuclear spins.
    >>further information

    • 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).
    Abstract--
    We study decoherence of nuclear spins in a GaAs quantum well structure using resistively detected NMR. In a tilted magnetic field, the decoherence is enhanced by the direct dipole-dipole interactions between first nearest-neighbor nuclei. The results agree well with simple numerical calculations.

    • Nuclear spin population and its control toward initialization using an all-electrical sub-micron scale nuclear magnetic resonance device
      T. Ota, G. Yusa, N. Kumada, S. Miyashita, and Y. Hirayama
      Appl. Phys. Lett. 90, 102118 (2007).
    Abstract--
    We study the nuclear spin population in a GaAs quantum well structure and demonstrate its initialization using an all-electrical NMR device.

    • Effects of inversion asymmetry on electron-nuclear spin coupling in semiconductor heterostructures: A possible role of spin-orbit interactions
      K. Hashimoto, K. Muraki, N. Kumada, and Y. Hirayama
      Phys. Rev. Lett. 94, 146601 (2005).
    Abstract--
    We show that electron-nuclear spin coupling in semiconductor heterostructures is strongly modified by their potential inversion asymmetry. We suggest that even a very weak Rashba spin-orbit interaction can play a dominant role.

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