1,194 research outputs found
Alternating gradient photodetector
A far infrared (FIR) range responsive photodetector is disclosed. There is a substrate of degenerate germanium. A plurality of alternating impurity-band and high resistivity layers of germanium are disposed on the substrate. The impurity-band layers have a doping concentration therein sufficiently high to include donor bands which can release electrons upon impingement by FIR photons of energy hv greater than an energy gap epsilon. The high resistivity layers have a doping concentration therein sufficiently low as to not include conducting donor bands and are depleted of electrons. Metal contacts are provided for applying an electrical field across the substrate and the plurality of layers. In the preferred embodiment as shown, the substrate is degenerate n-type (N++) germanium; the impurity-band layers are n+ layers of germanium doped to approximately the low 10(exp 16)/cu cm range; and, the high resistivity layers are n-layers of germanium doped to a maximum of approximately 10(exp)/cu cm. Additionally, the impurity-band layers have a thickness less than a conduction-electron diffusion length in germanium and likely to be in the range of 0.1 to 1.0 micron, the plurality of impurity-bands is of a number such that the flux of FIR photons passing therethrough will be substantially totally absorbed therein, the thickness of the high resistivity layers is such compared to the voltage applied that the voltage drop in each the high resistivity layers controls the occurence of impact ionization in the impurity-band layers to a desired level
P-wave Pairing and Colossal Magnetoresistance in Manganese Oxides
We point out that the existing experimental data of most manganese oxides
show the {\sl frustrated} p-wave superconducting condensation in the
ferromagnetic phase in the sense that the superconducting coherence is not long
enough to cover the whole system. The superconducting state is similar to the
state in superfluid He-3. The sharp drop of resistivity, the steep jump
of specific heat, and the gap opening in tunneling are well understood in terms
of the p-wave pairing. In addition, colossal magnetoresistance (CMR) is
naturally explained by the superconducting fluctuations with increasing
magnetic fields. The finite resistivity may be due to some magnetic
inhomogeneities. This study leads to the possibility of room temperature
superconductivity.Comment: LaTex, 14 pages, For more information, please send me an e-mail.
e-mail adrress : [email protected]
Surface Phason-Polaritons in Charge Density Wave Films
The coupled non-radiative excitations of the electromagnetic field and
phasons in films with a quasi one-dimensional charge density wave (CDW) are
evaluated for P--polarization and CDW conducting axis inside the film. The
prominent features are two surface phason-polariton branches extending from the
CDW pinning frequency to the frequency of the longitudinal optical phason.
These surface phason-polariton states are confined to a finite band of
longitudinal wave numbers. Besides surface polaritons, infinite series of
guided wave modes are found which extend to large wave numbers. These
differences to usual phonon-polaritons are caused by the extreme anisotropy of
the electric CDW reponse. This new class of surface polaritons is expected to
be found in the submillimeter frequency range.Comment: Latex2e, 18 pages, to be published in J. Phys. Chem. Solid
Corrections to Fermi's Golden Rule in Decays
We analyze the decays utilizing a formulation of
transition rates which explicitly exhibits corrections to Fermi's Golden Rule.
These corrections arise in systems in which the phase space and/or matrix
element varies rapidly with energy, as happens in , which is
just above threshold. We show that the theoretical corrections resolve a
puzzling discrepancy between theory and experiment for the branching
ratio
Comparison of the non-uniform chiral and 2SC phases at finite temperatures and densities
We study the phase diagram of the strongly interacting matter at finite
temperatures and densities including 2SC, uniform chiral and non-uniform chiral
phases within the Nambu - Jona-Lasinio model in the mean field approximation.Comment: 11 pages, 4 figures, to appear in Phys. Lett.
Broken Symmetry in Density-Functional Theory: Analysis and Cure
We present a detailed analysis of the broken-symmetry mean-field solutions
using a four-electron rectangular quantum dot as a model system. Comparisons of
the density-functional theory predictions with the exact ones show that the
symmetry breaking results from the single-configuration wave function used in
the mean-field approach. As a general cure we present a scheme that
systematically incorporates several configurations into the density-functional
theory and restores the symmetry. This cure is easily applicable to any
density-functional approach.Comment: 4 pages, 4 figures, submitted to PR
Do the A4c60 Fullerides Have a Broken-Symmetry Ground State?
Band theory predicts both K3C60 and K4C60 to be metals; various experimental
probes show that while K3C60 is indeed metallic, K4C60 appears to be
insulating. The standard view of this apparent failure of the single-particle
picture is that electron correlation is predominant. We describe an alternative
scenario, motivated on theoretical grounds, which invokes a spin- or
charge-density-wave state to explain the observed insulating behavior.Comment: 9 pages + 3 figures, REVTeX 3.
Thermoelectric Flux in Superconducting Rings
Definitive measurements by Van Harlingen et al. in 1980 show that the flux induced by a temperature difference across the two junctions of a Pb-In ring exceeds theoretical expectation by a factor, ϳ105. The theory fails owing to ͑mis͒use of a Boltzmann transport equation to describe the thermal diffusion of quasi-particle excitations, a treatment which violates electron conservation. An electron-conserving transport theory is developed and explains the data
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