192 research outputs found
On the cellular autoimmune mechanism for eliminating erythrocytes normally and under extreme influences
The presence of an autoimmune cellular mechanism for destroying erythrocytes on the basis of results of experiments in vivo is demonstrated in the blood and the organs. This mechanism is made up of a population of immunocompetent killer-lymphocytes which originates in the bone marrow and the thymus, and which is manifested in the local hemolysis effect
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
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
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
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
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
Filling factor dependence of the fractional quantum Hall effect gap
We directly measure the chemical potential jump in the low-temperature limit
when the filling factor traverses the nu = 1/3 and nu = 2/5 fractional gaps in
two-dimensional (2D) electron system in GaAs/AlGaAs single heterojunctions. In
high magnetic fields B, both gaps are linear functions of B with slopes
proportional to the inverse fraction denominator, 1/q. The fractional gaps
close partially when the Fermi level lies outside. An empirical analysis
indicates that the chemical potential jump for an IDEAL 2D electron system, in
the highest accessible magnetic fields, is proportional to q^{-1}B^{1/2}
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