368 research outputs found
Nonlocal transport near the charge neutrality point in a two-dimensional electron-hole system
Nonlocal resistance is studied in a two-dimensional system with a
simultaneous presence of electrons and holes in a 20 nm HgTe quantum well. A
large nonlocal electric response is found near the charge neutrality point
(CNP) in the presence of a perpendicular magnetic field. We attribute the
observed nonlocality to the edge state transport via counter propagating chiral
modes similar to the quantum spin Hall effect at zero magnetic field and
graphene near Landau filling factor Comment: 5 pages, 4 figure
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
Direct measurements of the fractional quantum Hall effect gaps
We measure the chemical potential jump across the fractional gap in the
low-temperature limit in the two-dimensional electron system of GaAs/AlGaAs
single heterojunctions. In the fully spin-polarized regime, the gap for filling
factor nu=1/3 increases LINEARLY with magnetic field and is coincident with
that for nu=2/3, reflecting the electron-hole symmetry in the spin-split Landau
level. In low magnetic fields, at the ground-state spin transition for nu=2/3,
a correlated behavior of the nu=1/3 and nu=2/3 gaps is observed
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
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
Dilute electron gas near the metal-insulator transition in two dimensions
In recent years systematic experimental studies of the temperature dependence
of the resistivity in a variety of dilute, ultra clean two dimensional
electron/hole systems have revived the fundamental question of localization or,
alternatively, the existence of a metal-insulator transition in the presence of
strong electron-electron interactions in two dimensions. We argue that under
the extreme conditions of ultra clean systems not only is the electron-electron
interaction very strong but the role of other system specific properties are
also enhanced. In particular, we emphasize the role of valleys in determining
the transport properties of the dilute electron gas in silicon inversion layers
(Si-MOSFETs). It is shown that for a high quality sample the temperature
behavior of the resistivity in the region close to the critical region of the
metal-insulator transition is well described by a renormalization group
analysis of the interplay of interaction and disorder if the electron band is
assumed to have two distinct valleys. The decrease in the resistivity up to
five times has been captured in the correct temperature interval by this
analysis, without involving any adjustable parameters. The considerable
variance in the data obtained from different Si-MOSFET samples is attributed to
the sample dependent scattering rate across the two valleys, presenting thereby
with a possible explanation for the absence of universal behavior in Si-MOSFET
samples of different quality
Magnetic-Field-Induced Hybridization of Electron Subbands in a Coupled Double Quantum Well
We employ a magnetocapacitance technique to study the spectrum of the soft
two-subband (or double-layer) electron system in a parabolic quantum well with
a narrow tunnel barrier in the centre. In this system unbalanced by gate
depletion, at temperatures T\agt 30 mK we observe two sets of quantum
oscillations: one originates from the upper electron subband in the
closer-to-the-gate part of the well and the other indicates the existence of
common gaps in the spectrum at integer fillings. For the lowest filling factors
and , both the common gap presence down to the point of one- to
two-subband transition and their non-trivial magnetic field dependences point
to magnetic-field-induced hybridization of electron subbands.Comment: Major changes, added one more figure, the latest version to be
published in JETP Let
Weak anisotropy and disorder dependence of the in-plane magnetoresistance in high mobility (100) Si-inversion layers
We report studies of the magnetoresistance (MR) in a two-dimensional electron
system in (100) Si-inversion layers, for perpendicular and parallel
orientations of the current with respect to the magnetic field in the 2D-plane.
The magnetoresistance is almost isotropic; this result does not support the
suggestion of the orbital origin of the MR in Si-inversion layer. In the
hopping regime, however, the MR contains a weak anisotropic component that is
non-monotonic in magnetic field. We found that the field, at which the MR
saturates, for different samples varies by a factor of two, being lower or
higher than the field of complete spin polarization of free carriers.
Therefore, the saturation of the MR can not be identified with the spin
polarization of free carriers.Comment: 4 pages, 4 figures; New data adde
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