S. Kozumi

Simultaneous excitation of spins and pseudospins in the bilayer ν=1 quantum Hall state

The tilting angular dependence of the energy gap was measured in the bilayer quantum Hall state at the Landau level filling v = 1 by changing the density imbalance between the two layers. The observed gap behavior shows acontinuous transformation from the bilayer balanced density state to the monolayer state. Even a sample with 33 K tunneling gap shows the same activation energy anomaly reported by Murphy et al. (Phys. Rev. Lett. 72 (1994) 728). We discuss a possible relation between our experimental results and the quantum Hall ferromagnet of spins and pseudospins.

Magnetotransport study of the canted antiferromagnetic phase in bilayer nu=2 quantum Hall state

Magnetotransport properties are investigated in the bilayer quantum Hall state at the total filling factor

DOUBLE MAGNETORESISTANCE MINIMA INDUCED BY THE IN-PLANE MAGNETIC FIELD FOR THE ν=1 DOUBLE-LAYER QUANTUM HALL STATE

\ensuremath{\nu}=2

Activation study of the pseudospin soliton in the v = 1 bilayer quantum Hall effect

. We measured the activation energy elaborately as a function of the total electron density and the density difference between the two layers. Our experimental data demonstrate clearly the emergence of the canted antiferromagnetic (CAF) phase between the ferromagnetic phase and the spin-singlet phase. The stability of the CAF phase is discussed by the comparison between experimental results and theoretical calculations using a Hartree-Fock approximation and an exact diagonalization study. The data reveal also an intrinsic structure of the CAF phase divided into two regions according to the dominancy between the intralayer and interlayer correlations.

Effects of In‐plane Magnetic Fields on the Canted Antiferromagnetic Phase in the Bilayer ν = 2 Quantum Hall State

We have investigated ν=1 quantum Hall (QH) state in a double-layer system around the commensurate (C) -incommensurate (IC) transition. Detailed magnetoresistance measurements around the C-IC transition reveal that there are two minima within the ν=1 QH state. These minima, being induced by the difference of the in-plane magnetic field, correspond to the C and IC phases, respectively. The region between the two minima may be the soliton lattice phase predicted by theoretical analyses.

Magnetoresistance Peak in the ν = 2 Bilayer Quantum Hall State under Tilted Magnetic Field

We study thermal excitations of the pseudospin soliton phase in the bilayer quantum Hall (QH) state at total Landau level filling factor v = 1. Near the commensurate-incommensurate phase transition point in the bilayer v = 1 QH state, we have found anomalous magnetotransport phenomena, such as the magnetoresistance peak and its anisotropic transport, which are ascribed to the formation of the pseudospin soliton phase (A. Fukuda et al., Phys. Rev. Lett. 100, 016801 (2008)). In this work, we elaborately measured activation energy gap Δ of the bilayer v = 1 QH state. Δ shows a broad minimum in the pseudospin soliton phase between the commensurate and incommensurate phase. We suggest that the minimum in Δ is due to collective modes of the pseudospin solitons forming a lattice.

Double magnetoresistance minima for v = 1 quantum Hall state near commensurate‐incommensurate transition

We investigate effects of an in‐plane magnetic field B∥ on the canted antiferromagnetic phase in the ν = 2 bilayer quantum Hall (QH) state by the magnetotransport measurements under tilted magnetic fields. We elaborately measure the activation energy of the ν = 2 bilayer QH state as a function of the total density nT for several tilting angles. We build up the phase diagram of the ν = 2 bilayer QH state in the B∥ − nT plane.

Microwave cavity perturbation technique for measurements of the quantum Hall effect

A bilayer quantum Hall (QH) state is a fascinating system which is constructed by adding the layer degree of freedom, which is represented as “pseudospin”, to an ordinary monolayer QH system. As a result of the combination of both spins and pseudospins, the ν = 2 bilayer QH state has revealed a variety of quantum phases. Recently the magnetoresistance peak was found in the ν = 1 bilayer QH state around the commensurate‐incommensurate (C‐IC) transition point. In this work we have carried out similar quantum magnetotranport experiments in the ν = 2 bilayer QH state while tilting a sample in a magnetic field. Although no anomalous behavior in magnetoresistance was found below the tilting angle of θC = 61°, a peak has been observed above θC. This structure resembles the peak reported in the ν = 1 QH state, and we expect it to be a signal of a phase transition in the ν = 2 QH state. We analyze this anomaly whether it results from the level crossing or the C‐IC transition.

Pseudospin domain of ν=1 double-layer quantum Hall state near commensurate–incommensurate transition

We investigated the v = 1 quantum Hall (QH) state in a double layer system around the commensurate (C) — incommensurate (IC) transition point. Around the phase transition, two magnetoresistance Rxx minima were observed for v = 1. The minimum observed at the lower magnetic field corresponds to the C phase and the other to the IC phase, respectively. From the temperature dependence of Rxx, we found that the miximum between the two minima remains finite even at the low temperature limit. This fact suggests that there is a dissipative phase between the C and IC states such as the theoretically predicted soliton lattice phase.