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
    clear
    • 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).
    Abstract--
    We investigate the electron spin states in the bilayer quantum Hall system at nu=2 exploiting current-pumped and resistively detected NMR. The results provide direct information on the spin configuration in this system and comprise strong evidence for the spin canting suggested by previous experiments.
    >>further information

    • Low-Frequency Spin Dynamics in a Canted Antiferromagnet
      N. Kumada, K. Muraki, and Y. Hirayama
      Science 313, 329 (2006). [full text]
    Abstract--
    Resistively-detected nuclear spin relaxation measurements in closely separated two-dimensional electron systems reveal strong low-frequency electron-spin fluctuations in the quantum Hall regime. Our data demonstrate the realization of a two-dimensional system with planar broken symmetry, in which fluctuations do not freeze out when approaching the zero temperature limit.
    >>further information

    • Doubly enhanced skyrmions in nu=2 bilayer quantum Hall states
      N. Kumada, A. Sawada, E. F. Ezawa, H. Azuhata, S. Nagahama, K. Muraki, T. Saku, and Y. Hirayama
      J. Phys. Soc. Jpn. 69, 3178 (2000).
    Abstract--
    We compare Skyrmion excitations in the bilayer QH state at nu_T=2 and in the single-layer QH state at nu=1. Difference in the number of flipped spin in a Skyrmion is interpreted to be due to the interlayer exchange interaction.

  • Bilayer quantum Hall state at nu=2/3

  • Control of nuclear spins in semiconductors

  • Other topics