204 research outputs found
Photoluminescence rings in Corbino disk at quantizing magnetic fields
Spatially resolved photoluminescence of modulation doped AlGaAs/GaAs
heterojunction was investigated in a sample of Corbino disk geometry subject to
strong perpendicular magnetic fields. Significant spatial modulation of the
photoluminescence was observed in form of one or more concentric rings which
travelled across the sample when the magnetic field strength was varied. A
topology of the observed structure excludes the possibility of being a trace of
an external current. The effect is attributed to formation of compressible and
incompressible stripes in a 2DEG density gradient across the sample.Comment: 5 two-column pages, 4 figures (one of them in color
Spin gap in the 2D electron system of GaAs/AlGaAs single heterojunctions in weak magnetic fields
We study the interaction-enhanced spin gaps in the two-dimensional electron
gas confined in GaAs/AlGaAs single heterojunctions subjected to weak magnetic
fields. The values are obtained from the chemical potential jumps measured by
magnetocapacitance. The gap increase with parallel magnetic field indicates
that the lowest-lying charged excitations are accompanied with a single spin
flip at the odd-integer filling factor nu=1 and nu=3, in disagreement with the
concept of skyrmions.Comment: as publishe
Spin magnetization of strongly correlated electron gas confined in a two-dimensional finite lattice
The influence of disorder and interaction on the ground state polarization of
the two-dimensional (2D) correlated electron gas is studied by numerical
investigations of unrestricted Hartree-Fock equations. The ferromagnetic ground
state is found to be plausible when the electron number is lowered and the
interaction and disorder parameters are suitably chosen. For a finite system at
constant electronic density the disorder induced spin polarization is cut off
when the electron orbitals become strongly localized to the individual network
sites. The fluctuations of the interaction matrix elements are calculated and
brought out as favoring the ferromagnetic instability in the extended and weak
localization regime. The localization effect of the Hubbard interaction term is
discussed.Comment: 7 pages, 9 figure
Quantum Hall effect at low magnetic fields
The temperature and scale dependence of resistivities in the standard scaling
theory of the integer quantum Hall effect is discussed. It is shown that recent
experiments, claiming to observe a discrepancy with the global phase diagram of
the quantum Hall effect, are in fact in agreement with the standard theory. The
apparent low-field transition observed in the experiments is identified as a
crossover due to weak localization and a strong reduction of the conductivity
when Landau quantization becomes dominant.Comment: 4 pages, 2 figures, minor corrections, to appear in PR
Indication of the ferromagnetic instability in a dilute two-dimensional electron system
The magnetic field B_c, in which the electrons become fully spin-polarized,
is found to be proportional to the deviation of the electron density from the
zero-field metal-insulator transition in a two-dimensional electron system in
silicon. The tendency of B_c to vanish at a finite electron density suggests a
ferromagnetic instability in this strongly correlated electron system.Comment: 4 pages, postscript figures included. Revised versio
Analysis of negative magnetoresistance. Statistics of closed paths. II. Experiment
It is shown that a new kind of information can be extracted from the Fourier
transform of negative magnetoresistance in 2D semiconductor structures. The
procedure proposed provides the information on the area distribution function
of closed paths and on the area dependence of the average length of closed
paths. Based on this line of attack the method of analysis of the negative
magnetoresistance is suggested. The method has been used to process the
experimental data on negative magnetoresistance in 2D structures with different
relations between the momentum and phase relaxation times. It is demonstrated
this fact leads to distinction in the area dependence of the average length of
closed paths.Comment: 5 pages, 5 figures, to be published in Phys.Rev.
Observation of the parallel-magnetic-field-induced superconductor-insulator transition in thin amorphous InO films
We study the response of a thin superconducting amorphous InO film with
variable oxygen content to a parallel magnetic field. A field-induced
superconductor-insulator transition (SIT) is observed that is very similar to
the one in normal magnetic fields. As the boson-vortex duality, which is the
key-stone of the theory of the field-induced SIT, is obviously absent in the
parallel configuration, we have to draw conclusion about the theory
insufficiency.Comment: 3 pages, 4 figure
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