1,780 research outputs found
Activation mechanisms in sodium-doped Silicon MOSFETs
We have studied the temperature dependence of the conductivity of a silicon
MOSFET containing sodium ions in the oxide above 20 K. We find the impurity
band resulting from the presence of charges at the silicon-oxide interface is
split into a lower and an upper band. We have observed activation of electrons
from the upper band to the conduction band edge as well as from the lower to
the upper band. A possible explanation implying the presence of Hubbard bands
is given.Comment: published in J. Phys. : Condens. Matte
Disorder and electron interaction control in low-doped silicon metal-oxide-semiconductor field effect transistors
We fabricated silicon metal-oxide-semiconductor field effect transistors
where an additional sodium-doped layer was incorporated into the oxide to
create potential fluctuations at the Si-SiO2 interface. The amplitude of these
fluctuations is controlled by both the density of ions in the oxide and their
position relative to the Si-SiO2 interface. Owing to the high mobility of the
ions at room temperature, it is possible to move them with the application of a
suitable electric field. We show that, in this configuration, such a device can
be used to control both the disorder and the electron-electron interaction
strength at the Si-SiO2 interface.Comment: 3 pages, 2 figure
Evidence for multiple impurity bands in sodium-doped silicon MOSFETs
We report measurements of the temperature-dependent conductivity in a silicon
metal-oxide-semiconductor field-effect transistor that contains sodium
impurities in the oxide layer. We explain the variation of conductivity in
terms of Coulomb interactions that are partially screened by the proximity of
the metal gate. The study of the conductivity exponential prefactor and the
localization length as a function of gate voltage have allowed us to determine
the electronic density of states and has provided arguments for the presence of
two distinct bands and a soft gap at low temperature.Comment: 4 pages; 5 figures; Published in PRB Rapid-Communication
The effect of screening long-range Coulomb interactions on the metallic behavior in two-dimensional hole systems
We have developed a technique utilizing a double quantum well heterostructure
that allows us to study the effect of a nearby ground-plane on the metallic
behavior in a GaAs two-dimensional hole system (2DHS) in a single sample and
measurement cool-down, thereby maintaining a constant disorder potential. In
contrast to recent measurements of the effect of ground-plane screening of the
long-range Coulomb interaction in the insulating regime, we find surprisingly
little effect on the metallic behavior when we change the distance between the
2DHS and the nearby ground-plane.Comment: 5 pages, 4 figures, accepted for publication in PR
The Psychopharmacology of Agitation: Consensus Statement of the American Association for Emergency Psychiatry Project BETA Psychopharmacology Workgroup
Agitation is common in the medical and psychiatric emergency department, and appropriate management of agitation is a core competency for emergency clinicians. In this article, the authors review the use of a variety of first-generation antipsychotic drugs, second-generation antipsychotic drugs, and benzodiazepines for treatment of acute agitation, and propose specific guidelines for treatment of agitation associated with a variety of conditions, including acute intoxication, psychiatric illness, delirium, and multiple or idiopathic causes. Pharmacologic treatment of agitation should be based on an assessment of the most likely cause of the agitation. If agitation results from a delirium or other medical condition, clinicians should first attempt to treat the underlying cause instead of simply medicating with antipsychotics or benzodiazepines
Variation of the hopping exponent in disordered silicon MOSFETs
We observe a complex change in the hopping exponent value from 1/2 to 1/3 as
a function of disorder strength and electron density in a sodium-doped silicon
MOSFET. The disorder was varied by applying a gate voltage and thermally
drifting the ions to different positions in the oxide. The same gate was then
used at low temperature to modify the carrier concentration.
Magnetoconductivity measurements are compatible with a change in transport
mechanisms when either the disorder or the electron density is modified
suggesting a possible transition from a Mott insulator to an Anderson insulator
in these systems.Comment: 6 pages, 5 figure
Nuclear spin coherence in a quantum wire
We have observed millisecond-long coherent evolution of nuclear spins in a
quantum wire at 1.2 K. Local, all-electrical manipulation of nuclear spins is
achieved by dynamic nuclear polarization in the breakdown regime of the Integer
Quantum Hall Effect combined with pulsed Nuclear Magnetic Resonance. The
excitation thresholds for the breakdown are significantly smaller than what
would be expected for our sample and the direction of the nuclear polarization
can be controlled by the voltage bias. As a four-level spin system, the device
is equivalent to two qubits.Comment: 5 pages, 5 figure
The Mystery of the Missing Boundary Layer
The question of the nature of the ultraviolet and X-ray radiation field of cataclysmic binaries is addressed. The spectrum and luminosity of this radiation are important in determining the mass transfer rate and energy budget of the system and in studies of the ejecta surrounding novae. In many systems, the soft X-ray luminosity is ~ 102-104 times weaker than predicted by simple accretion models. We discuss several possible solutions to this discrepancy. The most likely are either that the optical luminosity of a typical old nova is produced partly by reprocessed ultraviolet light from the white dwarf, or that the boundary layer, where accreted matter settles onto the white dwarf is both larger and more complicated than predicted by existing accretion disk models. The solution to this problem is of fundamental importance to accretion disk theory and will have implications for the study of most aspects of these systems, including models of the nova outburst itself
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