1,072 research outputs found
On the effect of far impurities on the density of states of two-dimensional electron gas in a strong magnetic field
The effect of impurities situated at different distances from a
two-dimensional electron gas on the density of states in a strong magnetic
field is analyzed. Based on the exact result of Brezin, Gross, and Itzykson, we
calculate the density of states in the whole energy range, assuming the Poisson
distribution of impurities in the bulk. It is shown that in the case of small
impurity concentration the density of states is qualitatively different from
the model case when all impurities are located in the plane of the
two-dimensional electron gas.Comment: 6 pages, 1 figure, submitted to JETP Letter
Effect of in-plane magnetic field on the photoluminescence spectrum of modulation-doped quantum wells and heterojunctions
The photoluminescence (PL) spectrum of modulation-doped GaAs/AlGaAs quantum
wells (MDQW) and heterojunctions (HJ) is studied under a magnetic field
() applied parallel to the two-dimensional electron gas (2DEG) layer.
The effect of strongly depends on the electron-hole separation
(), and we revealed remarkable -induced modifications of the PL
spectra in both types of heterostructures. A model considering the direct
optical transitions between the conduction and valence subband that are shifted
in k-space under , accounts qualitatively for the observed spectral
modifications. In the HJs, the PL intensity of the bulk excitons is strongly
reduced relatively to that of the 2DEG with increasing . This means
that the distance between the photoholes and the 2DEG decreases with increased
, and that free holes are responsible for the hole-2DEG PL.Comment: 6pages, 5figure
Theory of Phonon Shakeup Effects on Photoluminescence from the Wigner Crystal in a Strong Magnetic Field
We develop a method to compute shakeup effects on photoluminescence from a
strong magnetic field induced two-dimensional Wigner crystal. Only localized
holes are considered. Our method treats the lattice electrons and the tunneling
electron on an equal footing, and uses a quantum-mechanical calculation of the
collective modes that does not depend in any way on a harmonic approximation.
We find that shakeup produces a series of sidebands that may be identified with
maxima in the collective mode density of states, and definitively distinguishes
the crystal state from a liquid state in the absence of electron-hole
interaction. In the presence of electron-hole interaction, sidebands also
appear in the liquid state coming from short-range density fluctuations around
the hole. However, the sidebands in the liquid state and the crystal state have
different qualitative behaviors. We also find a shift in the main luminescence
peak, that is associated with lattice relaxation in the vicinity of a vacancy.
The relationship of the shakeup spectrum with previous mean-field calculations
is discussed.Comment: 14 pages, uuencoded postscript file for entire paper, also available
at (click phd14) http://rainbow.uchicago.edu/~ldz/paper/paper.htm
Harmonic Solid Theory of Photoluminescence in the High Field Two-Dimensional Wigner Crystal
Motivated by recent experiments on radiative recombination of two-dimensional
electrons in acceptor doped GaAs-AlGaAs heterojunctions as well as the success
of a harmonic solid model in describing tunneling between two-dimensional
electron systems, we calculate within the harmonic approximation and the time
dependent perturbation theory the line shape of the photoluminescence spectrum
corresponding to the recombination of an electron with a hole bound to an
acceptor atom. The recombination process is modeled as a sudden perturbation of
the Hamiltonian for the in-plane degrees of freedom of the electron. We include
in the perturbation, in addition to changes in the equilibrium positions of
electrons, changes in the curvatures of the harmonically approximated
potential. The computed spectra have line shapes similar to that seen in a
recent experiment. The spectral width, however, is roughly a factor of 3
smaller than that seen in experiment if one assumes a perfect Wigner crystal
for the initial state state of the system, whereas a simple random disorder
model yields a width a factor of 3 too large. We speculate on the possible
mechanisms that may lead to better quantitative agreement with experiment.Comment: 22 pages, RevTex, 8 figures. Submitted to the Physical Review
Goldstone Mode Relaxation in a Quantum Hall Ferromagnet due to Hyperfine Interaction with Nuclei
Spin relaxation in quantum Hall ferromagnet regimes is studied. As the
initial non-equilibrium state, a coherent deviation of the spin system from the
direction is considered and the breakdown of this Goldstone-mode
state due to hyperfine coupling to nuclei is analyzed. The relaxation occurring
non-exponentially with time is studied in terms of annihilation processes in
the "Goldstone condensate" formed by "zero spin excitons". The relaxation rate
is calculated analytically even if the initial deviation is not small. This
relaxation channel competes with the relaxation mechanisms due to spin-orbit
coupling, and at strong magnetic fields it becomes dominating.Comment: 8 page
Temperature dependence of spin polarizations at higher Landau Levels
We report our results on temperature dependence of spin polarizations at
in the lowest as well as in the next higher Landau level that compare
well with recent experimental results. At , except having a much smaller
magnitude the behavior of spin polarization is not much influenced by higher
Landau levels. In sharp contrast, for filling factor we predict
that unlike the case of the system remains fully spin polarized
even at vanishingly small Zeeman energies.Comment: 4 pages, REVTEX, and 3 .ps files, To be published in Physical Review
Letter
Upper bounds on the density of states of single Landau levels broadened by Gaussian random potentials
We study a non-relativistic charged particle on the Euclidean plane R^2
subject to a perpendicular constant magnetic field and an R^2-homogeneous
random potential in the approximation that the corresponding random Landau
Hamiltonian on the Hilbert space L^2(R^2) is restricted to the eigenspace of a
single but arbitrary Landau level. For a wide class of Gaussian random
potentials we rigorously prove that the associated restricted integrated
density of states is absolutely continuous with respect to the Lebesgue
measure. We construct explicit upper bounds on the resulting derivative, the
restricted density of states. As a consequence, any given energy is seen to be
almost surely not an eigenvalue of the restricted random Landau Hamiltonian.Comment: 16 pages, to appear in "Journal of Mathematical Physics
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