650 research outputs found
Shot noise in the interacting resonance level model
The shot noise power and the Fano factor of a spinless resonant level model
is calculated. The Coulomb interaction which in this model acts between the
lead electron and the impurity is considered in the first order approximation.
The logarithmic divergencies which appeared in the expressions for shot noise
and the transport current are removed by renormalization group analysis. It is
shown that Keldysh technique gives an adequate description of perturbation
theory results. By passing to the bosonized form of the resonance model it is
proven that in the strong interaction limit the tunnelling becomes irrelevant
and decreases.Comment: 4 pages, 2 figure
Expansion of a Bose-Einstein Condensate in the Presence of Disorder
Expansion of a Bose-Einstein condensate (BEC) is studied, in the presence of
a random potential. The expansion is controlled by a single parameter,
, where is the chemical potential, prior to the
release of the BEC from the trap, and is a transport relaxation
time which characterizes the strength of the disorder. Repulsive interactions
(nonlinearity) facilitate transport and can lead to diffusive spreading of the
condensate which, in the absence of interactions, would have remained localized
in the vicinity of its initial location
Boundary Energies and the Geometry of Phase Separation in Double--Exchange Magnets
We calculate the energy of a boundary between ferro- and antiferromagnetic
regions in a phase separated double-exchange magnet in two and three
dimensions. The orientation dependence of this energy can significantly affect
the geometry of the phase-separated state in two dimensions, changing the
droplet shape and possibly stabilizing a striped arrangement within a certain
range of the model parameters. A similar effect, albeit weaker, is also present
in three dimensions. As a result, a phase-separated system near the percolation
threshold is expected to possess intrinsic hysteretic transport properties,
relevant in the context of recent experimental findings.Comment: 6 pages, including 4 figures; expanded versio
Magnetotransport of coupled electron-holes
The carriers in InAs-GaSb double quantum wells are hybrid ``electron-holes''.
We study the magnetotransport properties of such particles using a
two-component Keldysh technique, which results in a semi-analytic expression
for the small-field current. We show that zero temperature current can be large
even when the Fermi energy lies within the hybridization gap, a result which
cannot be understood within a semiclassical (Boltzmann) approach. Magnetic
field dependence of the conductance is also affected significantly by the
hybridization of electrons and holes.Comment: 4 pages, 2 figure
Quantum oscillations in graphene in the presence of disorder and interactions
Quantum oscillations in graphene is discussed. The effect of interactions are
addressed by Kohn's theorem regarding de Haas-van Alphen oscillations, which
states that electron-electron interactions cannot affect the oscillation
frequencies as long as disorder is neglected and the system is sufficiently
screened, which should be valid for chemical potentials not very close to the
Dirac point. We determine the positions of Landau levels in the presence of
potential disorder from exact transfer matrix and finite size diagonalization
calculations. The positions are shown to be unshifted even for moderate
disorder; stronger disorder, can, however, lead to shifts, but this also
appears minimal even for disorder width as large as one-half of the bare
hopping matrix element on the graphene lattice. Shubnikov-de Haas oscillations
of the conductivity are calculated analytically within a self-consistent Born
approximation of impurity scattering. The oscillatory part of the conductivity
follows the widely invoked Lifshitz-Kosevich form when certain mass and
frequency parameters are properly interpreted.Comment: Appendix A was removed, as the content of it is already contained in
Ref. 17. Thanks to M. A. H. Vozmedian
The effect of electronic entropy on temperature peculiarities of the frequency characteristics of two interacting anharmonic vibrational modes in Zr
A 2D temperature-dependent effective potential is calculated for the
interacting longitudinal and transverse phonons of zirconium in the
frozen-phonon model. The effective potentials obtained for different
temperatures are used for the numerical solution of a set of stochastic
differential equations with a thermostat of the white-noise type. Analysis of
the spectral density of transverse vibrations allows one to determine the
temperature at which -Zr becomes unstable with respect to the
longitudinal vibrations. The obtained temperature value practically
coincides with the experimental temperature of the
structural transition in zirconium. The role of electronic entropy in the
Zr stability is discussed.Comment: 9 pages, 10 figures (submitted in Phys.Rev.
Runaway Quarks
When heavy nuclei collide, a quark-gluon plasma is formed. The plasma is
subject to strong electric field due to the charge of the colliding nuclei. The
electric field can influence the behavior of the quark-gluon plasma. In
particular, we might observe an increased number of quarks moving in the
direction of that field, as we do in the standard electron-ion plasma. In this
paper we show that this phenomenon, called the runaway quarks, does not exist.Comment: 13 pages, uses harvmac.tex, epsf.te
Non-meanfield deterministic limits in chemical reaction kinetics far from equilibrium
A general mechanism is proposed by which small intrinsic fluctuations in a
system far from equilibrium can result in nearly deterministic dynamical
behaviors which are markedly distinct from those realized in the meanfield
limit. The mechanism is demonstrated for the kinetic Monte-Carlo version of the
Schnakenberg reaction where we identified a scaling limit in which the global
deterministic bifurcation picture is fundamentally altered by fluctuations.
Numerical simulations of the model are found to be in quantitative agreement
with theoretical predictions.Comment: 4 pages, 4 figures (submitted to Phys. Rev. Lett.
Comment on "Clock Shift in High Field Magnetic Resonance of Atomic Hydrogen"
In this Comment, we reanalyze the experiments on the collision frequency
shift of the b-c and a-d hyperfine transitions in three-dimensional atomic
hydrogen in the presence of, respectively, a and b-state atoms. Accurate
consideration of the symmetry of the spatial and spin part of the diatomic
wavefunction yields the difference a_T-a_S=0.30(5) \AA between the triplet and
singlet s-wave scattering lengths of hydrogen atoms. This corrects the
factor-of two error of the commented work [Phys. Rev. Lett. 101, 263003
(2008)].Comment: 1 pag
Observation of the March Maximum in the Daemon Flux from Neos in the Year 2005: New Efforts and New Effects
The experiments of 2005 aimed at detection of low-velocity (~10-15 km s-1)
daemons falling on to the Earth's surface from Near-Earth, Almost Circular
Heliocentric Orbits (NEACHOs) have corroborated once more the existence of the
March maximum in their flux by raising its confidence level to 99.99%. In
addition, these experiments permitted us to identify several FEU-167-1-type PM
tubes, with a few times thicker inner Al coating, which appear to be capable to
detect, without any scintillator, the crossing of negatively charged daemons.
As a result, detection efficiency increases tens of times, thus raising the
measured level of the March daemon flux to f > 0.5E-7 cm-2s-1.Comment: 14 page
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