315 research outputs found
Opening an energy gap in an electron double layer system at integer filling factor in a tilted magnetic field
We employ magnetocapacitance measurements to study the spectrum of a double
layer system with gate-voltage-tuned electron density distributions in tilted
magnetic fields. For the dissipative state in normal magnetic fields at filling
factor and 4, a parallel magnetic field component is found to give rise
to opening a gap at the Fermi level. We account for the effect in terms of
parallel-field-caused orthogonality breaking of the Landau wave functions with
different quantum numbers for two subbands.Comment: 4 pages, 4 figures included, to appear in JETP Letter
Metal-insulator transition in a two-dimensional electron system: the orbital effect of in-plane magnetic field
The conductance of an open quench-disordered two-dimensional (2D) electron
system subject to an in-plane magnetic field is calculated within the framework
of conventional Fermi liquid theory applied to actually a three-dimensional
system of spinless electrons confined to a highly anisotropic (planar)
near-surface potential well. Using the calculation method suggested in this
paper, the magnetic field piercing a finite range of infinitely long system of
carriers is treated as introducing the additional highly non-local scatterer
which separates the circuit thus modelled into three parts -- the system as
such and two perfect leads. The transverse quantization spectrum of the inner
part of the electron waveguide thus constructed can be effectively tuned by
means of the magnetic field, even though the least transverse dimension of the
waveguide is small compared to the magnetic length. The initially finite
(metallic) value of the conductance, which is attributed to the existence of
extended modes of the transverse quantization, decreases rapidly as the
magnetic field grows. This decrease is due to the mode number reduction effect
produced by the magnetic field. The closing of the last current-carrying mode,
which is slightly sensitive to the disorder level, is suggested as the origin
of the magnetic-field-driven metal-to-insulator transition widely observed in
2D systems.Comment: 19 pages, 7 eps figures, the extension of cond-mat/040613
Quantization of the Hall conductivity well beyond the adiabatic limit in pulsed magnetic fields
We measure the Hall conductivity, , on a Corbino geometry sample
of a high-mobility AlGaAs/GaAs heterostructure in a pulsed magnetic field. At a
bath temperature about 80 mK, we observe well expressed plateaux in
at integer filling factors. In the pulsed magnetic field, the
Laughlin condition of the phase coherence of the electron wave functions is
strongly violated and, hence, is not crucial for quantization.Comment: 4 pages, 4 figures, submitted to PR
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
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
Equilibration between edge states in the fractional quantum Hall effect regime at high imbalances
We experimentally study equilibration between edge states, co-propagating at
the edge of the fractional quantum Hall liquid, at high initial imbalances. We
find an anomalous increase of the conductance between the fractional edge
states at the filling factor in comparison with the expected one for
the model of independent edge states. We conclude that the model of independent
fractional edge states is not suitable to describe the experimental situation
at .Comment: 4 page
Metal-insulator transition in a 2D electron gas: Equivalence of two approaches for determining the critical point
The critical electron density for the metal-insulator transition in a
two-dimensional electron gas can be determined by two distinct methods: (i) a
sign change of the temperature derivative of the resistance, and (ii) vanishing
activation energy and vanishing nonlinearity of current-voltage characteristics
as extrapolated from the insulating side. We find that in zero magnetic field
(but not in the presence of a parallel magnetic field), both methods give
equivalent results, adding support to the existence of a true zero-field
metal-insulator transition.Comment: As publishe
Temperature-Dependence of the Resistivity of a Dilute 2D Electron System in High Parallel Magnetic Field
We report measurements of the resistance of silicon MOSFETs as a function of
temperature in high parallel magnetic fields where the 2D system of electrons
has been shown to be fully spin-polarized. A magnetic field suppresses the
metallic behavior observed in the absence of a magnetic field. In a field of
10.8 T, insulating behavior is found for densities up to n_s approximately 1.35
x 10^{11} cm^{-2} or 1.5 n_c; above this density the resistance is a very weak
function of temperature, varying less than 10% between 0.25 K and 1.90 K. At
low densities the resistance goes to infinity more rapidly as the temperature
is reduced than in zero field and the magnetoresistance diverges as T goes to
0.Comment: 4 pages, including 4 figures. References adde
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