165 research outputs found
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
Canted antiferromagnetic phase in a double quantum well in a tilted quantizing magnetic field
We investigate the double-layer electron system in a parabolic quantum well
at filling factor in a tilted magnetic field using capacitance
spectroscopy. The competition between two ground states is found at the Zeeman
splitting appreciably smaller than the symmetric-antisymmetric splitting.
Although at the transition point the system breaks up into domains of the two
competing states, the activation energy turns out to be finite, signaling the
occurrence of a new insulator-insulator quantum phase transition. We interpret
the obtained results in terms of a predicted canted antiferromagnetic phase.Comment: 4 pages, 3 figures included, accepted to PR
Hybridization of electron subbands in a double quantum well at quantizing magnetic field
We employ magnetocapacitance and far-infrared spectroscopy techniques to
study the spectrum of the double-layer electron system in a parabolic quantum
well with a narrow tunnel barrier in the centre. For gate-bias-controlled
asymmetric electron density distributions in this soft two-subband system we
observe both individual subband gaps and double layer gaps at integer filling
factor . The bilayer gaps are shown to be either trivial common for two
subbands or caused by hybridization of electron subbands in magnetic field. We
describe the observed hybrid gaps at and within a simple model
for the modified bilayer spectrum.Comment: REVTeX, 24 pages, 9 figures included. Submitted to Phys. Rev.
Sharply increasing effective mass: a precursor of the spontaneous spin polarization in a dilute two-dimensional electron system
We have measured the effective mass, m, and Lande g-factor in very dilute
two-dimensional electron systems in silicon. Two independent methods have been
used: (i) measurements of the magnetic field required to fully polarize the
electrons' spins and (ii) analysis of the Shubnikov-de Haas oscillations. We
have observed a sharp increase of the effective mass with decreasing electron
density while the g-factor remains nearly constant and close to its value in
bulk silicon. The corresponding strong rise of the spin susceptibility may be a
precursor of a spontaneous spin polarization; unlike in the Stoner scenario, it
originates from the enhancement of the effective mass rather than the increase
of g-factor. Furthermore, using tilted magnetic fields, we have found that the
enhanced effective mass is independent of the degree of spin polarization and,
therefore, its increase is not related to spin exchange effects, in
contradiction with existing theories. Our results show that the dilute 2D
electron system in silicon behaves well beyond a weakly interacting Fermi
liquid.Comment: This paper summarizes results reported in our recent publications on
the subjec
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
Pauli spin susceptibility of a strongly correlated two-dimensional electron liquid
Thermodynamic measurements reveal that the Pauli spin susceptibility of
strongly correlated two-dimensional electrons in silicon grows critically at
low electron densities - behavior that is characteristic of the existence of a
phase transition.Comment: As publishe
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
On the Electron-Electron Interactions in Two Dimensions
In this paper, we analyze several experiments that address the effects of
electron-electron interactions in 2D electron (hole) systems in the regime of
low carrier density. The interaction effects result in renormalization of the
effective spin susceptibility, effective mass, and g*-factor. We found a good
agreement among the data obtained for different 2D electron systems by several
experimental teams using different measuring techniques. We conclude that the
renormalization is not strongly affected by the material or sample-dependent
parameters such as the potential well width, disorder (the carrier mobility),
and the bare (band) mass. We demonstrate that the apparent disagreement between
the reported results on various 2D electron systems originates mainly from
different interpretations of similar "raw" data. Several important issues
should be taken into account in the data processing, among them the dependences
of the effective mass and spin susceptibility on the in-plane field, and the
temperature dependence of the Dingle temperature. The remaining disagreement
between the data for various 2D electron systems, on one hand, and the 2D hole
system in GaAs, on the other hand, may indicate more complex character of
electron-electron interactions in the latter system.Comment: Added refs; corrected typos. 19 pages, 7 figures. To be published in:
Chapter 19, Proceedings of the EURESCO conference "Fundamental Problems of
Mesoscopic Physics ", Granada, 200
Classical effects in the weak-field magnetoresistance of InGaAs/InAlAs quantum wells
We observe an unusual behavior of the low-temperature magnetoresistance of
the high-mobility two-dimensional electron gas in InGaAs/InAlAs quantum wells
in weak perpendicular magnetic fields. The observed magnetoresistance is
qualitatively similar to that expected for the weak localization and
anti-localization but its quantity exceeds significantly the scale of the
quantum corrections. The calculations show that the obtained data can be
explained by the classical effects in electron motion along the open orbits in
a quasiperiodic potential relief manifested by the presence of ridges on the
quantum well surface
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