D. Terasawa

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.

Continuous transformation from spin- to pseudospin-type excitation

Abstract We measured the activation energy of bilayer ν=1 quantum Hall states. By changing the density difference between layers, the tilting behavior of the pseudospin(P)-type activation energy at the equal density point gradually transforms into the spin(S)-type one at the monolayer density point. At the intermediate density difference, by increasing the tilting angle the activation energy starts to decrease as the P-type excitation gap and then increases as the S-type excitation gap. It is impossible to explain this behavior by the level crossing of the P- and S-type excitations. The result of the overall behavior indicates the excitation in a bilayer system is the simultaneous flip of spin and pseudospin.

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

Various phase transitions in bilayer quantum Hall states

. 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.

Interlayer diffusion of nuclear spin polarization inν=23quantum Hall states

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.

Effects of the In‐plane Magnetic Fields on Excitations of the ν = 1/3 Bilayer Quantum Hall States in the Vicinity of Single Layer Limit

AbstractWe measured the magnetoresistance in bilayer quantum Hall (QH) state at fractional lling factor = 23 . Surprisingly,for dierent QH areas and two types of hysteresis were observed by controlling the total electron density and the densitydierenceintwolayers.TwoQHareasandonetypeofhysteresisarenovelcharacteristicofbilayersystems. ? 2002ElsevierScienceB.V.Allrightsreserved. PACS:73.43.Np;73.43.Qt;73.40.KpKeywords:FractionalquantumHalleect;GaAs =AlGaAs;Bilayer system; Composite fermion ThebilayerquantumHall(QH)statehasattractedagreatdealofrecentattention,wherethestructurein-troducesadditionaldegreesoffreedominthethird(z)direction. In this system, spin-split Landau levels(LLs) further split in the bonding and antibondingstates of electron wave functions localized in eachlayer. It is convenient to use pseudospin language,wherepseudospinP z = 12 (P z = − 12 )referstoanelec-troninthefront(back)layer.Atthellingfactor =2,the competition between the pseudospin-Zeeman ef-fectandtheZeemaneectleadstoaphasetransitionbetween the spin-polarized and the spin-unpolarizedstates [1–5]. However, only a few researches havebeen done at bilayer fractional QH eects [6]. The2=

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

At the spin transition point of

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

\nu=2/3

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

quantum Hall states, nuclear spins in a two-dimensional electron gas are polarized by an electric current. Using GaAs/AlGaAs double-quantum-well samples, we first observed the spatial diffusion of nuclear spin polarization between the two layers when the nuclear spin polarization is current-induced in one layer. By numerical simulation, we estimated the diffusion constant of the nuclear spin polarization to be