290 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
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.
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
Strongly enhanced effective mass in dilute two-dimensional electron systems: System-independent origin
We measure the effective mass in a dilute two-dimensional electron system in
(111)-silicon by analyzing temperature dependence of the Shubnikov-de Haas
oscillations in the low-temperature limit. A strong enhancement of the
effective mass with decreasing electron density is observed. The mass
renormalization as a function of the interaction parameter r_s is in good
agreement with that reported for (100)-silicon, which shows that the relative
mass enhancement is system- and disorder-independent being determined by
electron-electron interactions only.Comment: As publishe
Anisotropic positive magnetoresistance of a nonplanar 2D electron gas in a parallel magnetic field
We study the transport properties of a 2D electron gas in narrow GaAs quantum
wells with AlAs/GaAs superlattice barriers. It is shown that the anisotropic
positive magnetoresistance observed in selectively doped semiconductor
structures in a parallel magnetic field is caused by the spatial modulation of
the 2D electron gas.Comment: 4 pages, 3 figure
Magnetoresistance of a two-dimensional electron gas in a parallel magnetic field
The conductivity of a two-dimensional electron gas in a parallel magnetic
field is calculated. We take into account the magnetic field induced
spin-splitting, which changes the density of states, the Fermi momentum and the
screening behavior of the electron gas. For impurity scattering we predict a
positive magnetoresistance for low electron density and a negative
magnetoresistance for high electron density. The theory is in qualitative
agreement with recent experimental results found for Si inversion layers and Si
quantum wells.Comment: 4 pages, figures included, PDF onl
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
THE EGALITARIAN PRINCIPLES OF THE OLD BOHEMIAN STATEHOOD AND THE LEGAL SYSTEM
Purpose: The article is devoted to the study of egalitarian principles of medieval Czech statehood and the legal system.
Methods: The authors pay special attention to the peculiarities of family self-government of the Czech communities, the institution of hazing in land law and the mechanism of reconciliation as an alternative to the death penalty.
Findings: The paper proves that tribal remnants of the customary law of the ancient Czech people in the medieval era contributed to the preservation of egalitarian democratic principles of public administration and justice
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
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