1,094 research outputs found
Dynamic density functional study of a driven colloidal particle in polymer solutions
The Dynamic Density Functional (DDF) theory and standard Brownian dynamics
simulations (BDS) are used to study the drifting effects of a colloidal
particle in a polymer solution, both for ideal and interacting polymers. The
structure of the stationary density distributions and the total induced current
are analyzed for different drifting rates. We find good agreement with the BDS,
which gives support to the assumptions of the DDF theory. The qualitative
aspect of the density distribution are discussed and compared to recent results
for driven colloids in one-dimensional channels and to analytical expansions
for the ideal solution limit
Geometric Bogomolov conjecture for abelian varieties and some results for those with some degeneration (with an appendix by Walter Gubler: The minimal dimension of a canonical measure)
In this paper, we formulate the geometric Bogomolov conjecture for abelian
varieties, and give some partial answers to it. In fact, we insist in a main
theorem that under some degeneracy condition, a closed subvariety of an abelian
variety does not have a dense subset of small points if it is a non-special
subvariety. The key of the proof is the study of the minimal dimension of the
components of a canonical measure on the tropicalization of the closed
subvariety. Then we can apply the tropical version of equidistribution theory
due to Gubler. This article includes an appendix by Walter Gubler. He shows
that the minimal dimension of the components of a canonical measure is equal to
the dimension of the abelian part of the subvariety. We can apply this result
to make a further contribution to the geometric Bogomolov conjecture.Comment: 30 page
Semiclassical action based on dynamical mean-field theory describing electrons interacting with local lattice fluctuations
We extend a recently introduced semiclassical approach to calculating the
influence of local lattice fluctuations on electronic properties of metals and
metallic molecular crystals. The effective action of electrons in degenerate
orbital states coupling to Jahn-Teller distortions is derived, employing
dynamical mean-field theory and adiabatic expansions. We improve on previous
numerical treatments of the semiclassical action and present for the
simplifying Holstein model results for the finite temperature optical
conductivity at electron-phonon coupling strengths from weak to strong.
Significant transfer of spectral weight from high to low frequencies is
obtained on isotope substitution in the Fermi-liquid to polaron crossover
regime.Comment: 10 pages, 7 figure
Indications of coherence-incoherence crossover in layered transport
For many layered metals the temperature dependence of the interlayer
resistance has a different behavior than the intralayer resistance. In order to
better understand interlayer transport we consider a concrete model which
exhibits this behavior. A small polaron model is used to illustrate how the
interlayer transport is related to the coherence of quasi-particles within the
layers. Explicit results are given for the electron spectral function,
interlayer optical conductivity and the interlayer magnetoresistance. All these
quantities have two contributions: one coherent (dominant at low temperatures)
and one incoherent (dominant at high temperatures).Comment: 6 pages, 4 figures, REVTEX
Exactly solvable path integral for open cavities in terms of quasinormal modes
We evaluate the finite-temperature Euclidean phase-space path integral for
the generating functional of a scalar field inside a leaky cavity. Provided the
source is confined to the cavity, one can first of all integrate out the fields
on the outside to obtain an effective action for the cavity alone.
Subsequently, one uses an expansion of the cavity field in terms of its
quasinormal modes (QNMs)-the exact, exponentially damped eigenstates of the
classical evolution operator, which previously have been shown to be complete
for a large class of models. Dissipation causes the effective cavity action to
be nondiagonal in the QNM basis. The inversion of this action matrix inherent
in the Gaussian path integral to obtain the generating functional is therefore
nontrivial, but can be accomplished by invoking a novel QNM sum rule. The
results are consistent with those obtained previously using canonical
quantization.Comment: REVTeX, 26 pages, submitted to Phys. Rev.
Holstein model in infinite dimensions at half-filling
The normal state of the Holstein model is studied at half-filling in infinite
dimensions and in the adiabatic regime. The dynamical mean-field equations are
solved using perturbation expansions around the extremal paths of the effective
action for the atoms. We find that the Migdal-Eliashberg expansion breaks down
in the metallic state if the electron-phonon coupling exceeds a value
of about 1.3 in spite of the fact that the formal expansion parameter ( is the phonon frequency, the Fermi energy) is
much smaller than 1. The breakdown is due to the appearance of more than one
extremal path of the action. We present numerical results which illustrate in
detail the evolution of the local Green's function, the self-energy and the
effective atomic potential as a function of .Comment: Revtex + 17 postscript figures include
Photoconductance Quantization in a Single-Photon Detector
We have made a single-photon detector that relies on photoconductive gain in
a narrow electron channel in an AlGaAs/GaAs 2-dimensional electron gas. Given
that the electron channel is 1-dimensional, the photo-induced conductance has
plateaus at multiples of the quantum conductance 2e/h. Super-imposed on
these broad conductance plateaus are many sharp, small, conductance steps
associated with single-photon absorption events that produce individual
photo-carriers. This type of photoconductive detector could measure a single
photon, while safely storing and protecting the spin degree of freedom of its
photo-carrier. This function is valuable for a quantum repeater that would
allow very long distance teleportation of quantum information.Comment: 4 pages, 4 figure
Synthesis, structural and physical properties of -FeSe
We report on synthesis, structural characterization, resistivity, magnetic
and thermal expansion measurements on the as yet unexplored -phase of
FeSe, here synthesized under ambient- (AP) and high-pressure (HP)
conditions. We show that in contrast to -FeSe, monophasic
superconducting -FeSe can be obtained in off-stoichiometric
samples with excess Fe atoms preferentially residing in the van der Waals gap
between the FeSe layers. The AP -FeSe sample studied here
( 8.5\,K) possesses an unprecedented residual resistivity ratio
RRR 16. Thermal expansion data reveal a small feature around
90\,K, which resembles the anomaly observed at the structural and
magnetic transitions for other Fe-based superconductors, suggesting that some
kind of "magnetic state" is formed also in FeSe. %indicative of a fluctuating
magnetic ordering. For HP samples (RRR 3), the disorder within the
FeSe layers is enhanced through the introduction of vacancies, the saturated
magnetic moment of Fe is reduced and only spurious superconductivity is
observed.Comment: 7 pages, 8 figures, published versio
The Holstein Polaron
We describe a variational method to solve the Holstein model for an electron
coupled to dynamical, quantum phonons on an infinite lattice. The variational
space can be systematically expanded to achieve high accuracy with modest
computational resources (12-digit accuracy for the 1d polaron energy at
intermediate coupling). We compute ground and low-lying excited state
properties of the model at continuous values of the wavevector in
essentially all parameter regimes. Our results for the polaron energy band,
effective mass and correlation functions compare favorably with those of other
numerical techniques including DMRG, Global Local and exact diagonalization. We
find a phase transition for the first excited state between a bound and unbound
system of a polaron and an additional phonon excitation. The phase transition
is also treated in strong coupling perturbation theory.Comment: 24 pages, 11 figures submitted to PR
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