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
    • Resonant Edge Magnetoplasmons and Their Decay in Graphene
      N. Kumada, P. Roulleau, B. Roche, M. Hashisaka, H. Hibino, I. Petkovic, and D. C. Glattli
      Phys. Rev. Lett. 113, 266601 (2014).
    We investigate resonant edge magnetoplasmons (EMPs) and their decay in graphene by high-frequency electronic measurements. From EMP resonances in disk shaped graphene, we show that the dispersion relation of EMPs is nonlinear due to interactions, giving rise to the intrinsic decay of EMP wave packets. We also identify extrinsic dissipation mechanisms due to interaction with localized states in bulk graphene from the decay time of EMP wave packets. Owing to the linear band structure and the sharp edge potential, EMP dissipation in graphene can be lower than that in GaAs systems.

    • Plasmon transport and its guiding in graphene
      Norio Kumada, Romain Dubourget, Ken'ichi Sasaki, Shinichi Tanabe, Hiroki Hibino, Hiroshi Kamata, Masayuki Hashisaka, Koji Muraki, Toshimasa Fujisawa
      New J. Phys. 16, 063055 (2014).
    Transport of plasmons in graphene has been investigated by time-resolved electrical measurements. We demonstrate plasmon guiding in a gate-defined pattern. An important advantage of the gate-defined waveguide is dynamical switching of guiding characteristics with the gate voltages.

    • Fractionalized wave packets from an artificial Tomonaga-Luttinger liquid
      H. Kamata, N. Kumada, M. Hashisaka, K. Muraki, and T. Fujisawa
      Nature Nanotechnology 9, 177 (2014).
    We report time-resolved transport measurements on an artificial Tomonaga-Luttinger liquid (TLL) composed of coupled integer quantum Hall edge channels. We show charge fractionalization, a hallmark of TLL, in which an injection of elementary charge e from a non-interacting lead is divided into the non-trivial effective charge e* and the remainder, e-e*.

    • Plasmon transport in graphene investigated by time-resolved electrical measurements
      N. Kumada, S. Tanabe, H. Hibino, H. Kamata, M. Hashisaka, K. Muraki, and T. Fujisawa
      Nature Commun. 4, 1363 (2013).
    We investigate edge magnetoplasmon (EMP) transport in graphene using time-resolved transport measurement. We demonstrate that the velocity of EMPs varies over two orders of magnitude by changing the carrier density, magnetic field, and gate screening effect.
    >>further information

    • Edge magnetoplasmon transport in gated and ungated quantum Hall systems
      N. Kumada, H. Kamata, and T. Fujisawa
      Phys. Rev. B 84, 045314 (2011).
    Edge magnetoplasmon (EMP) transport in gated and ungated quantum Hall systems is investigated by time-of-flight measurements. We measured the velocity, the amplitude, and the broadening of the EMP pulse injected by applying a voltage pulse to an Ohmic contact. We show that the transverse width of EMPs in the ungated sample is determined by the potential profile in the edge region, independent of the filling factor. In the gated sample, on the other hand, EMPs are confined by the innermost incompressible strip and their transverse width depends on the filling factor and the bulk electron density. We also find that scattering of EMPs by the bulk electrons is modified by the presence of the gate.
    >>further information

  • 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

  • Other topics