Showing papers on "Landau quantization published in 1988"
TL;DR: A two-dimensional condensed-matter lattice model is presented which exhibits a nonzero quantization of the Hall conductance in the absence of an external magnetic field, and exhibits the so-called "parity anomaly" of (2+1)-dimensional field theories.
Abstract: A two-dimensional condensed-matter lattice model is presented which exhibits a nonzero quantization of the Hall conductance ${\ensuremath{\sigma}}^{\mathrm{xy}}$ in the absence of an external magnetic field. Massless fermions without spectral doubling occur at critical values of the model parameters, and exhibit the so-called "parity anomaly" of (2+1)-dimensional field theories.
4,606 citations
TL;DR: L'existence d'une transition solide-liquide dans un plasma electronique bidimensionnel dans la limite quantique est etablie dans l'heterojonction GaAs'GaAlAs par detection d'un branche de magnetophonons sans bande interdite.
Abstract: The existence of the magnetic-field-induced liquid-to-solid phase transition in an extreme quantum-limit 2D electron plasma is established for electrons at a high-quality GaAs/GaAlAs heterojunction by detection of a gapless magnetophonon excitation branch with radio-frequency spectroscopy. The phase diagram, determined for Wigner-Seitz to Bohr radius ratio $1.6l{r}_{s}l2.5$, extrapolates to a zero-temperature critical Landau-level filling factor ${\ensuremath{
u}}_{c}=0.23\ifmmode\pm\else\textpm\fi{}0.04$ and a zero-filling-factor melting temperature close to the classical (${r}_{s}\ensuremath{\rightarrow}\ensuremath{\infty}$) limit.
302 citations
TL;DR: This work shows for AlGaAs/GaAs heterostructures how this finite spin splitting at B=0 evolves from the Zeeman splitting for B\ensuremath{
e}0 and predicts a vanishingspin splitting at a finite -magnetic- field \char22{}, which depends on the electron concentration in the inversion layer.
Abstract: Spin splitting of subband states in semiconductor heterostructures at B=0 is ascribed to the inversion asymmetry--induced bulk ${\mathrm{k}}^{3}$ term, which dominates in large-gap materials, and to the interface spin-orbit or Rashba term, which becomes important in narrow-gap systems. We show for AlGaAs/GaAs heterostructures how this finite spin splitting at B=0 evolves from the Zeeman splitting for B\ensuremath{
e}0 and predict a vanishing spin splitting at a finite -magnetic- field ---, which depends on the electron concentration in the inversion layer.
278 citations
TL;DR: La transition entre les etats propres localises et etendus en regime d'effet Hall quantique integral est un phenomene d'echelle dans l'etude du tenseur de magnetoconductivite en fonction of the temperature and du champ magnetique.
Abstract: The transition between localized and extended eigenstates in the integral quantum Hall regime is observable as a scaling phenomenon in the magnetoresistance tensor as a function of temperature and applied magnetic field strength. Field-theoretic studies on the quantum Hall effect are used to derive the scaling functions. The scaling behavior is shown to involve only a single critical exponent ($\ensuremath{\mu}$) which is the ratio between the inelastic-scattering exponent ($p$) and twice the localization length exponent ($\ensuremath{
u}$). The results have recently been confirmed experimentally.
226 citations
TL;DR: In this paper, an analytic wave function describing a spin-singlet incompressible fluid of electrons confined to a single Landau level was presented, which exhibits a half-integral quantum Hall effect.
Abstract: We present an analytic wave function describing a spin-singlet incompressible fluid of electrons confined to a single Landau level, which exhibits a half-integral quantum Hall effect. Our numerical studies suggest that this state may be responsible for the recently observed effect with \ensuremath{
u}=(5/2. .AE
196 citations
TL;DR: In this article, the density of states of 2DEG in the quantum Hall regime for heterostructures with a thick spacer was studied and it was shown that the spatial distribution of charged impurities should be correlated if a doped region is not entirely depleted.
78 citations
TL;DR: Magnetoquantum oscillations in the tunnel current of double-barrier n−GaAs/(AlGa)As/GaAs/AlGa As/GaA resonant tunneling devices reveal evidence of sequential tunneling in the voltage range corresponding to the resonance when electrons tunnel into the second subband of the GaAs quantum well.
Abstract: Magnetoquantum oscillations in the tunnel current of double‐barrier n‐GaAs/(AlGa)As/GaAs/(AlGa)As/GaAs resonant tunneling devices reveal evidence of sequential tunneling in the voltage range corresponding to the resonance when electrons tunnel into the second subband of the GaAs quantum well. The sequential tunneling arises from intersubband scattering between two quasi‐bound states of the well. Near this resonance, the charge buildup in the well can be estimated from the magnetoquantum oscillations.
72 citations
TL;DR: In this article, the screening properties of a two-dimensional electron gas (2D EG) in a quantizing magnetic field at low temperatures are calculated within the Hartree approximation, and strong nonlinear effects, such as perfect screening in only a part of the sample and pinning of the energy spectrum to the Fermi level, are observed.
Abstract: The screening properties of a two-dimensional electron gas (2D EG) in a quantizing magnetic field at low temperatures are calculated within the Hartree approximation. The effect of a periodic external potential on the equilibrium state is studied for two models of the 2D EG, a strictly two-dimensional Hall strip geometry and a three-dimensional model of a heterostructure without lateral confinement. The single-particle energy spectrum is found to depend drastically on the collective state of the 2D EG, i.e., the position of the Fermi energy with respect to the Landau levels. Strong nonlinear effects, such as perfect screening in only a part of the sample and pinning of the energy spectrum to the Fermi level, are observed.
65 citations
TL;DR: In this article, the radiative recombination of two-dimensional electrons with nonequilibrium photoexcited holes in the magnetic field has been investigated in single heterojunctions for the first time.
Abstract: The radiative recombination of two-dimensional electrons with nonequilibrium photoexcited holes in the magnetic field has been investigated in $\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}\ensuremath{-}{\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ single heterojunctions for the first time. Two different channels of radiative recombination are observed---a recombination with free holes and with the holes bound to acceptor atoms. In a magnetic field perpendicular to the two-dimensional (2D) layer, both luminescence lines are split into Landau levels, and these splittings depend only on the normal component of the magnetic field. It is shown that when the concentration of two-dimensional electrons is increased, the first excited two-dimensional subband is populated and an additional intense line appears in both components of the spectrum. The high intensity of this line originates from a considerable overlap of corresponding wave functions of 2D electrons and of the holes and enables one to investigate independently the properties of 2D electrons from the first excited subband.
61 citations
IBM1
TL;DR: In this paper, single particle relaxation time and the scattering time of the 2DEG in modulation doped GaAs/AlGaAs heterostructure are measured by Ladau respectively, for samples with spacer layer thickness 1.5-500 nm.
60 citations
TL;DR: In this paper, a theory of non-linear screening of a two-dimensional electron gas (2DEG) in a strong magnetic field and in a smooth random potential at T = 0 is presented.
TL;DR: In this article, an asymmetric resonant-tunnelling structure based on n-GaAs/(AlGa)As, incorporating a thin emitter barrier and a thick collector barrier, was observed to have intrinsic bistability.
Abstract: Intrinsic bistability is observed in an asymmetric resonant-tunnelling structure based on n-GaAs/(AlGa)As, incorporating a thin emitter barrier and a thick collector barrier. The resonant charge build-up in the quantum well which gives rise to the bistability is monitored by the Landau level structure in the magneto-capacitance.
TL;DR: The existence of fractional quantised Hall states in other than the lowest (n=0) Landau level is discussed in this article, where the authors present the results of numerical studies of systems with up to nine particles in the n=1 Landau-level.
Abstract: The authors discuss the existence of fractional quantised Hall states in other than the lowest (n=0) Landau level They present the results of numerical studies of systems with up to nine particles in the n=1 Landau level They find that a fractional quantised Hall state is likely for filling fractions of the n=1 Landau level, nu 1, with nu 1-1=5 At nu 1-1=3 they find that the Laughlin trial wavefunctions is not a good candidate ground-state wavefunction If there is a gap at nu 1-1 it is predicted to be small At nu 1-1=7/2 they predict the existence of a fractional quantised Hall state despite the small or non-existent gap at nu 1-1=3 They also show that introducing truncated pseudopotential interactions is not always a physical procedure outside of the lowest Landau level
TL;DR: It is shown that the theory applies to a much wider range of temperature than what was thought earlier, and an important controversy in the experimental literature is resolved.
Abstract: Theoretical results are obtained for the energy loss of hot electrons to longitudinal optical phonons in quasi-two-dimensional semiconductor systems for carrier temperatures between 25 and 200 K. Quantum statistics, dynamical screening, plasmon-phonon coupling, Landau damping, hot-phonon effects, and quantum-well-width corrections are included in a many-body calculation. The results are in good agreement with experiments. We resolve an important controversy in the experimental literature, as well as show that the theory applies to a much wider range of temperature than what was thought earlier.
TL;DR: A new selection rule is employed to determine simultaneously the optical effective masses of the electrons and in-plane light holes in n-type strained GaAs/InGaAs/AlGaAs quantum wells.
Abstract: We present experimental and theoretical evidence for impurity-assisted off-diagonal (i.e., ..delta..n>0) transitions between conduction- and valence-band Landau levels (n = 0,1,. . . ) for magnetoluminescence in modulation-doped degenerate semiconductor quantum wells. This new selection rule is employed to determine simultaneously the optical effective masses of the electrons and in-plane light holes in n-type strained GaAs/InGaAs/AlGaAs quantum wells.
TL;DR: In this paper, a relativistic extension of the Brueckner-Hartee-Fock model was proposed to obtain a microscopically derived quasiparticle interaction in the medium which is in reasonably close agreement with the empirical Landau interaction.
TL;DR: Very well resolved electron Landau levels (LLs) are observed in the photoluminescence spectra of modulation-doped InGaAsInP quantum wells as mentioned in this paper.
TL;DR: In qualitative agreement with a number of recent experimental findings, calculated level broadenings are much larger than that implied by the zero-field mobility.
Abstract: The density of states of a two-dimensional electron gas is calculated in the weak-disorder limit by taking into account self-consistent screening and Landau-level coupling effects. The resultant density of states is broad with considerable overlap between Landau levels, being strikingly different from the well-separated sharp levels of the standard short-range impurity-scattering model. In qualitative agreement with a number of recent experimental findings, calculated level broadenings are much larger than that implied by the zero-field mobility.
TL;DR: In this article, a review of the current theoretical concepts and experimental methods employed in studying the two-dimensional electron density of states in a magnetic field is presented, and the importance of the screening of random external potential fluctuations by 2D electrons and particularly the oscillatory dependence of screening on electron concentration is discussed.
Abstract: This review covers the current theoretical concepts and experimental methods employed in studying the two-dimensional electron density of states in a magnetic field. The authors discuss the different factors that determine the energy distribution of the density of states in real systems. They demonstrate the importance of the screening of random external potential fluctuations by two-dimensional electrons and particularly the oscillatory dependence of screening on electron concentration. When considering the various theoretical approaches and experimental methods, the authors analyze their conditions of applicability and the self-consistency of obtained results. They demonstrate that it is possible to evaluate experimentally the random potential amplitude and range from the oscillations in Landau level broadening.
TL;DR: In this paper, the cyclotron resonance of electrons in a GaAs/Ga0.64Al 0.36As multi-quantum well sample with 2.2 nm well width is reported, in magnetic fields up to 19 T applied perpendicular to the well planes.
TL;DR: The energy per particle of a two-dimensional electron system in the lowest Landau level is studied making use of the particle-hole symmetry and an accurate interpolation formula for the dependence of the energy on the filling factor is given.
Abstract: The energy per particle of a two-dimensional electron system in the lowest Landau level is studied making use of the particle-hole symmetry. An accurate interpolation formula for the dependence of the energy on the filling factor is given; the formula is compared with the results of finite-size calculations performed in the spherical geometry.
TL;DR: In this article, a quantum-transport theory of scattering within broadened Landau levels was proposed for the low-density, two-dimensional classical electron gas formed on the surface of liquid helium.
Abstract: Magnetoconductance measurements are reported for the low-density, two-dimensional classical electron gas formed on the surface of liquid helium. At strong magnetic fields, large deviations from the classical parabolic behaviour are observed. These deviations are described with a quantum-transport theory of scattering within broadened Landau levels.
TL;DR: Les regles de selection pour les transitions de Landau fournissent l'unique possibilite de determiner les frequences cyclotroniques des bandes de valence and des bande de conduction.
Abstract: Two-photon magnetoabsorption measurements in a GaAs-AlGaAs multiple quantum well are presented for the first time. With the use of high-power picosecond pulses from a ${\mathrm{CO}}_{2}$ laser and a tunable dye laser, Landau transitions are clearly resolved in magnetic fields up to 6.6 T. Two-photon selection rules for Landau transitions (\ensuremath{\Delta}n=\ifmmode\pm\else\textpm\fi{}1) give the unique possibility to determine the cyclotron frequencies of the valence band and conduction band separately.
TL;DR: In this paper, a GaAs-AlxGa1−xAs heterojunction was placed in close proximity to the surface of a piezoelectric substrate on which a surface acoustic wave was propagated.
TL;DR: In this article, the authors observed the breakdown of cyclotron resonance in large magnetic fields oriented perpendicular to the growth direction in semiconductor superlattices, and a model was proposed to account for the magnetic field dependence of the resonance position and line width.
TL;DR: In this article, the authors measured phonon scattering by a 2DEG in a Si MOSFET and showed quantum oscillations as the Fermi levels is moved through the Landau level spectrum.
TL;DR: In this paper, it was shown that the origin of the fractional quantum Hall effect is due to the same incompressible-quantum-fluid state which manifests itself at odd-denominator fractions.
Abstract: The recently discovered fractional quantum Hall effect at $\frac{5}{2}$ filling has been studied by the standard technique of finite electron systems in a periodic rectangular geometry. We have evaluated the low-lying excitations and the correlation functions for \textonehalf{} filling in the lowest Landau level, as well as in the next Landau level with the lowest Landau level fully filled. The results indicate that the origin of the $\frac{5}{2}$ effect is due to the same incompressible-quantum-fluid state which manifests itself at odd-denominator fractions.
TL;DR: It is shown that possible forms for the density matrices of states of a two-dimensional electron gas (2D EG) are profoundly limited when the electrons are constrained to lie in the lowest Landau level.
Abstract: We show that possible forms for the density matrices of states of a two-dimensional electron gas (2D EG) are profoundly limited when the electrons are constrained to lie in the lowest Landau level. In particular for any number of particles the matrices may be expressed in terms of their diagonal elements in a position representation. The simplification which is known to occur for Hartree-Fock calculations in a single Landau level of the 2D EG is a specific consequence of this general property.
TL;DR: In this article, the effect of nonmagnetic impurity scattering on the Landau-level width of a quasi-two-dimensional conductor was studied and it was shown that the square-root dependence of the landau level width on the magnetic field obtained by Ando and Uemura [J. Phys. Soc. Jpn. 36, 959 (1974)] in a two-dimensional electron gas crosses over to a (2/3) power law in a quasi 2D electron gas.
Abstract: The effect of nonmagnetic-impurity scattering on the Landau-level width in a quasi-two-dimensional conductor is studied. It is shown that the square-root dependence of the Landau-level width on the magnetic field obtained by Ando and Uemura [J. Phys. Soc. Jpn. 36, 959 (1974)] in a two-dimensional electron gas crosses over to a (2/3-power law in a quasi-two-dimensional electron gas.