<Japanese>

Organization

Department of Physics, Faculty of Science, University of Tokyo
Iye group at Institute for Solid State Physics, Univ. of Tokyo

Physics-Related Links

Former Studies

Transport of Two-dimensional Electron Gas in Random Magnetic Field

• Since 1998 at Iye-Katsumoto group (ISSP, Univ.of Tokyo)

1. M. Ando, A. Endo, S. Katsumoto and Y. Iye, LT22 International Conference (1999)
2. Doctoral Thesis(3.5MB) and its abstract in Japanese

Superconducting Network in Checkerboard Field

• 1999 at Iye-Katsumoto group (ISSP, Univ.of Tokyo)

1. M. Ando, S. Ito, S. Katsumoto and Y. Iye, J. Phys. Soc. Jpn. 68, 3462 (1999)
2. S. Ito, M. Ando, S. Katsumoto and Y. Iye, J. Phys. Soc. Jpn. 68, 3158 (1999)

Transport of Point Contact in Fractional Quantum Hall Regime

• Since Apr.1996 at Iye-Katsumoto group (ISSP, Univ.of Tokyo)

1. M. Ando, A. Endo, S. Katsumoto and Y. Iye, Solid State Electronics 42, 1179 (1998)
2. M. Ando, A. Endo, S. Katsumoto and Y. Iye, Physica B, 249-251, 426 (1998)

Many transport phenomena of integer quantum Hall effect can be understood in terms of edge channels with the use of Landauer-Buttiger formalism. However the edge channel picture for fractional quantum Hall effect(FQHE) is yet to be established.

We are studying experimentally the transport through point contacts in FQH states. A GaAs/AlGaAs 2D electron gas is put in a magnetic field, fixed to FQH states of filling factors 1 and 2/3. Negative voltage applied to the split gate defined on the sample varies the channel width of the Hall bar, which can be observed as a two terminal conductance. The gate voltage - conductance profile showed a series of fractionally quantized plateaus such as 1/5, 1/3, 2/3 and 4/5, which are different from the bulk filling factors 1 or 2/3.

Energy Spectra for Flat Bands in Strong Magnetic Fields

• Oct. 1995 - Mar. 1996 at Aoki group (Dept.of Physics, Univ.of Tokyo)

1. H. Aoki, M. Ando and H. Matsumura, Phys. Rev. B54, 17296 (1996) (or cond-mat/9607223)

Flat band or Dispersionless band is an energy band such that all Bloch states in the band have the same energy eigenvalue. Since this means that infinite number of states degenerate at this single energy eigenvalue, it is discussed as an possible model for itinerant ferromagnetism.

Whether a flat band maintains its flattness in magnetic fields, or whether Landau quantization occurs if it does becomes dispersive is the problem. On the other hand, energy spectrum for tight-binding square lattice in uniform magnetic field is known to possess a fractal structure and is called "Hofstadter diagram".

We have calculated the energy spectra for various two-dimensional tight-binding lattices with at least one flat bands in uniform magnetic fields and found that a flat band behaves differently in accordance with its origin: Magnetic fields preserve those flat bands that arise from topological reason, while dispersions emerge in a singular manner for the flat bands arising from interference.

Effects of Microwave on Transport in Tin Granular Films

• Apr.- July 1995 at Kobayashi-Ikehata group (Dept.of Physics, Univ.of Tokyo)