Research topics
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
    • 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).
    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]
    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).
    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