Yuichi Shimoda

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

Excitation spectrum of bilayer ν=2 quantum Hall systems

\ensuremath{\nu}=2

Modulation of bilayer quantum Hall states by tilted-field-induced subband-Landau-level coupling

. 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.

HARTREE–FOCK–BOGOLIUBOV STUDIES OF BILAYER ν = 2 QUANTUM HALL SYSTEMS

Abstract Excitation spectra in bilayer quantum Hall systems at total Landau-level filling ν =2 are studied by the Hartree–Fock–Bogoliubov approximation. The systems have the spin degrees of freedom in addition to the layer degrees of freedom described in terms of pseudospin. On the excitation spectra from spin-unpolarized and pseudospin-polarized ground state, this approximation fully preserves the spin rotational symmetry and thus can give not only spin-triplet but also spin-singlet excitations systematically. It is also found that the ground-state properties are well described by this approximation.

Various phase transitions in bilayer quantum Hall states

We study effects of tilted magnetic fields on energy levels in a double-quantum-well (DQW) system, focusing on the coupling of subbands and Landau levels (LLs). The subband-LL coupling induces anticrossings between LLs, manifested directly in the magnetoresistance. The anticrossing gap becomes larger than the spin splitting at the tilting angle � ∼ 20 ◦ and larger than the cyclotron energy at � ∼ 50 ◦ , demonstrating that the subband-LL coupling exerts a strong influence ⊥ +

Theoretical phase diagram of bilayer ν = 1 quantum Hall system

Excitation spectra in bilayer quantum Hall systems at total Landau-level filling ν = 2 are studied by the Hartree–Fock–Bogoliubov (HFB) approximation. The systems have the spin degrees of freedom in addition to the layer degrees of freedom described in terms of pseudospin. On the excitation spectrum from the spin-singlet and pseudospin-polarized ground state, this approximation fully preserves the spin rotational symmetry and thus can give both spin-triplet and spin-singlet excitations systematically. It is also found that the ground state is pseudospin squeezed because of pseudospin correlations and that the HFB approximation can describe ground-state properties better than other approximations.

GROUND-STATE PROPERTIES OF BILAYER ν=2 QUANTUM HALL STATES

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=

PHASE DIAGRAM OF THE ν = 2 BILAYER QUANTUM HALL STATE

We theoretically study the bilayer ν = 1 quantum Hall system under an inplane magnetic field. When the in-plane field becomes strong, interlayer coherence in the system is suppressed by the field and the ground state is expected to show a phase transition from a commensurate state to an incommensurate one. We investigate a phase diagram of this system by analyzing the mode-softening properties of the random-phase-approximation excitation spectrum. The diagram indicates another phase between these ones and shows a qualitatively good agreement with the one obtained by a recent experiment.

Erratum to: “Quantum transport study of canted antiferromagnetic phase in the ν=2 bilayer quantum Hall state”: [Physica E 34 (2006) 77]

We construct a Hartree-Fock-Bogoliubov (HFB) Hamiltonian Haldane-sphere and study excitation spectra and ground-state properties in bilayer ν=2 QH systems. It is found that the HFB approximation can systematically give SU(2) symmetrical excitation spectra spectra well agree with those from exact diagonalization calculations in large tunneling-energy region. In this region, has been considered to be a pseudospin-squeezed ground state is favored theory.