S. Komiyama

Temperature Limitations of Quantum Hall Far-Infrared Photodetectors

We have investigated the temperature, T, dependence of a highly sensitive far-infrared (FIR) photodetector fabricated on a two-dimensional electron gas system in GaAs/AlGaAs heterostructures. The photoinduced resistance change, ΔRxx, observed in different integer quantum Hall (QH) regimes shows different T dependences. At high T, ΔRxx is limited by the vanishing of rising electronic temperature ΔTe. For T < 5 K, ΔRxx can either rapidly increase with lower T or slowly diminish, determined by the interplay between the magnetic field dependence of ΔTe and the T dependence of QH states.

System-size dependence of quantum hall transitions

The quantum Hall plateau-to-insulator (plateau) transition is studied in small GaAs two-dimensional electron gas systems, where the system size L is comparable to or smaller than the correlation length L cor of potential fluctuation. At low temperatures, the transition depends on the system size but the dependence is not explained in terms of Anderson localization. At elevated temperatures, the transition width exhibits a power-law dependence but the exponent κ takes nonuniversal values. It is suggested that the transition crosses over from the well-known, Anderson localization dominated regime to the semiclassical percolation-dominated regime when the system size is reduced below L cor .

Transport properties of a quantum dot in quantum Hall regimes probed by a single-electron transistor

Coulomb blockade oscillations in a semiconductor quantum dot (QD) with two confined Landau levels are investigated by probing a current through a single-electron transistor (SET) fabricated directly on top of the QD. The intradot tunneling events between the compressible regions in the dot are mapped out by measuring SET currents. Our results demonstrate that a SET can be an excellent electrometer that is extremely responsive to the local individual electron tunneling events in a closed electronic system.

Nano‐Scale Probing of Edge Spin States via Nuclear Spin Polarization

Microscopy of electron spin states in edge channels are performed by using nuclear spin polarization as a sensitive local probe in the integer quantum Hall regime of the filling factor νbulk = 2. The nuclear polarization situated within the compressible region of 1<ν<2 is found to exhibit anomalous enhancement of the relaxation rate. The relaxation rate is crucially influenced by the magnetic field strength as well as the softness of the gate‐controlled confinement potential, suggesting that the ground state of the edge channels is the spin‐textured state.