5,721 research outputs found
Localized vibrational modes of lithium and lithium-defect pairs in silicon Final report, 1 Jul. 1967 - 30 Sep. 1968
Localized vibrational modes of lithium and lithium-defect pairs in silico
Localized vibration modes of defect pairs in silicon
Absorption bands and localized vibrational modes of silicon doped with boron compounds containing phosphorus, arsenic, antimony, or lithiu
A Special Case Of A Conjecture By Widom With Implications To Fermionic Entanglement Entropy
We prove a special case of a conjecture in asymptotic analysis by Harold
Widom. More precisely, we establish the leading and next-to-leading term of a
semi-classical expansion of the trace of the square of certain integral
operators on the Hilbert space . As already observed by Gioev and
Klich, this implies that the bi-partite entanglement entropy of the free Fermi
gas in its ground state grows at least as fast as the surface area of the
spatially bounded part times a logarithmic enhancement.Comment: 20 pages, 3 figures, improvement of the presentation, some references
added or updated, proof of Theorem 12 (formerly Lemma 11) adde
Chaotic itinerancy and power-law residence time distribution in stochastic dynamical system
To study a chaotic itinerant motion among varieties of ordered states, we
propose a stochastic model based on the mechanism of chaotic itinerancy. The
model consists of a random walk on a half-line, and a Markov chain with a
transition probability matrix. To investigate the stability of attractor ruins
in the model, we analyze the residence time distribution of orbits at attractor
ruins. We show that the residence time distribution averaged by all attractor
ruins is given by the superposition of (truncated) power-law distributions, if
a basin of attraction for each attractor ruin has zero measure. To make sure of
this result, we carry out a computer simulation for models showing chaotic
itinerancy. We also discuss the fact that chaotic itinerancy does not occur in
coupled Milnor attractor systems if the transition probability among attractor
ruins can be represented as a Markov chain.Comment: 6 pages, 10 figure
Evolution of the Dark Matter Distribution at the Galactic Center
Annihilation radiation from neutralino dark matter at the Galactic center
(GC) would be greatly enhanced if the dark matter were strongly clustered
around the supermassive black hole (SBH). The existence of a dark-matter
"spike" is made plausible by the observed, steeply-rising stellar density near
the GC SBH. Here the time-dependent equations describing gravitational
interaction of the dark matter particles with the stars are solved. Scattering
of dark matter particles by stars would substantially lower the dark matter
density near the GC SBH over 10^10 yr, due both to kinetic heating, and to
capture of dark matter particles by the SBH. This result suggests that
enhancements in the dark matter density around a SBH would be modest whether or
not the host galaxy had experienced the scouring effects of a binary SBH.Comment: 5 pages, 3 figures. Submitted to Physical Review Letter
Fermi Level Position at Semiconductor Surfaces
There have been several recent reports of barrier height studies on metal-semiconductor interfaces. Metals of widely different work functions evaporated onto Si and GaAs surfaces indicated that in each case the energy difference
between the semiconductor conduction band edge
and Fermi level at the interface,φ_(Bn), was essentially
independent of the metal, which indicates
that the Fermi level is fixed by surface
states. In the present work barrier height measurements
have been made on a number of zinc-blende semiconductors to determine (a) if the barriers are in all cases determined by surface states, and (b) the relation between the Fermi
energy at the interface and the band gap E_g
Trace formulas for Wiener-Hopf operators with applications to entropies of free fermionic equilibrium states
We consider non-smooth functions of (truncated) Wiener–Hopf type operators on the Hilbert space
L2(Rd)
. Our main results are uniform estimates for trace norms (
d≥1
) and quasiclassical asymptotic formulas for traces of the resulting operators (
d=1
). Here, we follow Harold Widom's seminal ideas, who proved such formulas for smooth functions decades ago. The extension to non-smooth functions and the uniformity of the estimates in various (physical) parameters rest on recent advances by one of the authors (AVS). We use our results to obtain the large-scale behaviour of the local entropy and the spatially bipartite entanglement entropy (EE) of thermal equilibrium states of non-interacting fermions in position space
Rd
(
d≥1
) at positive temperature,
T>0
. In particular, our definition of the thermal EE leads to estimates that are simultaneously sharp for small T and large scaling parameter
α>0
provided that the product Tα remains bounded from below. Here α is the reciprocal quasiclassical parameter. For
d=1
we obtain for the thermal EE an asymptotic formula which is consistent with the large-scale behaviour of the ground-state EE (at
T=0
), previously established by the authors for
d≥1
Photoemission from Au and Cu into CdS
Many metal-semiconductor surface barrier rectifiers
show photosensitivity for photon energies (hv) less than the semiconductor energy gap (E_g).
Cases in the literature include metals evaporated
or electrodeposited on elemental and III-V
compound semiconductor surfaces. In these studies
the source of the low-energy photocurrent, when
hv < E_g, was shown to be the photoemission of
carriers over the Schottky barrier between the metal
film and the semiconductor. An extensive investigation
has been reported for a series of metals,
particularly Cu and Au, electroplated on n-type CdS
with the conclusion that here also photoemission
from the metal is responsible for most of the low-energy photovoltage. However, recent studies have
questioned this conclusion for the CdS case. One
study proposed that the origin of the low-energy
photovoltaic response is electron photoexcitation
from Cu impurities located in the CdS and within a
diffusion length of the space charge region. Hole
conduction probably in the 3d Cu levels was postulated
for these samples, which had ≈ 30-ppm Cu. A second study interpreted the results as a p·n junction photovoltaic effect
Conduction Band Minima of Ga(As_(1−x)P_x)
Photoresponse of surface barriers on samples of Ga(As_(1−x_P_x) covering the range 0≤x≤1 has been measured. Thresholds corresponding to both direct and indirect band-to-band excitations within the semiconductor and also photoinjection from the metal have been identified. The threshold of the direct transition varies with composition from 1.37 eV in GaAs to 2.65 eV in GaP. The indirect transition was followed for x≳0.38 and again varied linearly from 2.2 eV in GaP to an extrapolated value in 1.62 eV in GaAs. The energy separation of the two conduction band minima in GaAs is in disagreement with previously reported values
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