8,332 research outputs found
Comment on "Theory of metal-insulator transitions in gated semiconductors" (B. L. Altshuler and D. L. Maslov, Phys. Rev. Lett. 82, 145 (1999))
In a recent Letter, Altshuler and Maslov propose a model which attributes the
anomalous temperature and field dependence of the resistivity of
two-dimensional electron (or hole) systems to the charging and discharging of
traps in the oxide (spacer), rather than to intrinsic behavior of interacting
particles associated with a conductor-insulator transition in two dimensions.
We argue against this model based on existing experimental evidence.Comment: 1 page; submitted to PR
Fire Protection Of Wooden Storage Containers For Explosive And Pyrotechnic Products
Analysis of the emergency storage facilities for explosive and pyrotechnic products is conducted. It is established that one of the greatest risks is their flammability. Since the explosive and pyrotechnic products are stored in wooden containers, there is a need for their fire protection. To determine the efficiency of fire resistant containers for packaging explosive products it is designed operating range of testing method. This method is necessary to establish mass loss, measuring the growth temperature and response time of the squibs. The results of the efficiency of the fire retardant treatment of wood and organic coated coating showed that when exposed to high–temperature destruction of the construction detonation of the squibs didn\u27t happen.Tests to determine the quality of the fire retardant treatment of wood coatings showed that the temperature on the inner surfaces of the untreated sample was more than 760 ºC, samples with fire retardant coatings – no more than 128 °C. The conclusion of the feasibility of using fire–retardants is not based on inorganic and organic binders for the treatment of wooden structures.Method of determining the fire protection is used to assess the efficiency of the fire protection of wooden structures. Method comprises determining the ratio of the sample rate of burnout, the temperature increment and the ignition time of untreated and treated samples. As a result of the firing testing it is established a speed burnout reduction of samples of the container with treated coatings compared with untreated coatings is decreased by 2,4-4,4 times and respectively fire protection efficiency factor of treated samples of the container compared to untreated is increased by1.8-4.1 times
Classical versus Quantum Effects in the B=0 Conducting Phase in Two Dimensions
In the dilute two-dimensional electron system in silicon, we show that the
temperature below which Shubnikov-de Haas oscillations become apparent is
approximately the same as the temperature below which an exponential decrease
in resistance is seen in B=0, suggesting that the anomalous behavior in zero
field is observed only when the system is in a degenerate (quantum) state. The
temperature dependence of the resistance is found to be qualitatively similar
in B=0 and at integer Landau level filling factors.Comment: 3 pages, 3 figure
Magnetic Field Suppression of the Conducting Phase in Two Dimensions
The anomalous conducting phase that has been shown to exist in zero field in
dilute two-dimensional electron systems in silicon MOSFETs is driven into a
strongly insulating state by a magnetic field of about 20 kOe applied parallel
to the plane. The data suggest that in the limit of T -> 0 the conducting phase
is suppressed by an arbitrarily weak magnetic field. We call attention to
striking similarities to magnetic field-induced superconductor-insulator
transitions
Superconductivity in correlated disordered two-dimensional electron gas
We calculate the dynamic effective electron-electron interaction potential
for a low density disordered two-dimensional electron gas. The disordered
response function is used to calculate the effective potential where the
scattering rate is taken from typical mobilities from recent experiments. We
investigate the development of an effective attractive pair potential for both
disordered and disorder free systems with correlations determined from existing
numerical simulation data. The effect of disorder and correlations on the
superconducting critical temperature Tc is discussed.Comment: 4 pages, RevTeX + epsf, 4 figure
Novel Properties of The Apparent Metal-Insulator Transition in Two-Dimensional Systems
The low-temperature conductivity of low-density, high-mobility,
two-dimensional hole systems in GaAs was studied. We explicitly show that the
metal-insulator transition, observed in these systems, is characterized by a
well-defined critical density, p_0c. We also observe that the low-temperature
conductivity of these systems depends linearly on the hole density, over a wide
density range. The high-density linear conductivity extrapolates to zero at a
density close to the critical density.Comment: 4 Figure
Spin polarization of strongly interacting 2D electrons: the role of disorder
In high-mobility silicon MOSFET's, the inferred indirectly from
magnetoconductance and magnetoresistance measurements with the assumption that
are in surprisingly good agreement with obtained by
direct measurement of Shubnikov-de Haas oscillations. The enhanced
susceptibility exhibits critical behavior of the form
. We examine the significance of the field
scale derived from transport measurements, and show that this field
signals the onset of full spin polarization only in the absence of disorder.
Our results suggest that disorder becomes increasingly important as the
electron density is reduced toward the transition.Comment: 4 pages, 3 figure
Scaling and the Metal-Insulator Transition in Si/SiGe Quantum Wells
The existence of a metal-insulator transition at zero magnetic field in two-
dimensional electron systems has recently been confirmed in high mobility
Si-MOSFETs. In this work, the temperature dependence of the resistivity of
gated Si/SiGe/Si quantum well structures has revealed a similar metal-
insulator transition as a function of carrier density at zero magnetic field.
We also report evidence for a Coulomb gap in the temperature dependence of
the resistivity of the dilute 2D hole gas confined in a SiGe quantum well.
In addition, the resistivity in the insulating phase scales with a single
parameter, and is sample independent. These results are consistent with the
occurrence of a metal-insulator transition at zero magnetic field in SiGe
square quantum wells driven by strong hole-hole interactions.Comment: 3 pages, 3 figures, LaTe
Spin Degree of Freedom in a Two-Dimensional Electron Liquid
We have investigated correlation between spin polarization and
magnetotransport in a high mobility silicon inversion layer which shows the
metal-insulator transition. Increase in the resistivity in a parallel magnetic
field reaches saturation at the critical field for the full polarization
evaluated from an analysis of low-field Shubnikov-de Haas oscillations. By
rotating the sample at various total strength of the magnetic field, we found
that the normal component of the magnetic field at minima in the diagonal
resistivity increases linearly with the concentration of ``spin-up'' electrons.Comment: 4 pages, RevTeX, 6 eps-figures, to appear in PR
Universal scaling, beta function, and metal-insulator transitions
We demonstrate a universal scaling form of longitudinal resistance in the
quantum critical region of metal-insulator transitions, based on numerical
results of three-dimensional Anderson transitions (with and without magnetic
field), two-dimensional quantum Hall plateau to insulator transition, as well
as experimental data of the recently discovered two-dimensional metal-insulator
transition. The associated reflection symmetry and a peculiar logarithmic form
of the beta function exist over a wide range in which the resistance can change
by more than one order of magnitude. Interesting implications for the
two-dimensional metal-insulator transition are discussed.Comment: 4 pages, REVTEX, 4 embedded figures; minor corrections to figures and
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