289 research outputs found
Mean field theory for driven domain walls in disordered environments
We study the mean field equation of motion for driven domain walls in random
media. We discuss the two cases of an external constant as well as an
oscillating driving force. Our main focus lies on the critical dynamics close
to the depinning transition, which we study by analytical and numerical
methods. We find power-law scaling for the velocity as well as the hysteresis
loop area.Comment: 16 pages, 19 figures, submitted to Phys. Rev.
Excitation spectrum of a 2D long-range Bose-liquid with a supersymmetry
We have studied excitation spectrum of the specfic 2D model of strongly
interacting Bose particles via mapping of the many-body Schrodinger equation in
imaginary time to the classical stochastic dynamics. In a broad range of
coupling strength a roton-like spectrum is found, with the roton gap
being extremely small in natural units. A single quantum phase transition
between strongly correlated supefluid and quantum Berezinsky crystal is found.Comment: 6 pages, 6 figure
Flavor Mixing, Neutrino Masses and Neutrino Oscillations
We study a model for the mass matrices of the leptons. We are ablte to relate
the mass eigenvalues of the charged leptons and of the neutrinos to the mxiing
angles and can predict the masses of the neutrinos. We find a normal hierarchy
-the masses are 0.004 eV, 0.01 eV and 0.05 eV. The atmospheric mixing angle is
given by the mass ratios of the charged leptons and of the neutrinos. We find
38 degrees, consistent with the experiments. The mixing element, connecting the
first neutrino with the electron, is found to be 0.05.Comment: 4 page
Possible mechanisms for initiating macroscopic left-right asymmetry in developing organisms
How might systematic left-right (L/R) asymmetry of the body plan originate in
multicellular animals (and plants)? Somehow, the microscopic handedness of
biological molecules must be brought up to macroscopic scales. Basic symmetry
principles suggest that the usual "biological" mechanisms -- diffusion and gene
regulation -- are insufficient to implement the "right-hand rule" defining a
third body axis from the other two. Instead, on the cellular level, "physical"
mechanisms (forces and collective dynamic states) are needed involving the long
stiff fibers of the cytoskeleton. I discuss some possible scenarios; only in
the case of vertebrate internal organs is the answer currently known (and even
that is in dispute).Comment: 9 pp latex, 6 figures. Proc. Landau 100 Memorial Conf.
(Chernogolovka, June 2008); to appear AIP Conf. series. (v2: added 4 ref's +
revised Sec 2.2.
Statistical physics of dyons and quark confinement
We present a semiclassical approach to the SU(N) Yang--Mills theory whose
partition function at nonzero temperatures is approximated by a saddle point --
an ensemble of an infinite number of interacting dyons of N kinds. The ensemble
is governed by an exactly solvable 3d quantum field theory, allowing
calculation of correlations functions relevant to confinement. We show that
known criteria of confinement are satisfied in this semiclassical
approximation: (i) the average Polyakov line is zero below some critical
temperature, and nonzero above it, (ii) a quark-antiquark pair has linear
rising potential energy, (iii) the average spatial Wilson loop falls off
exponentially with the area, (iv) N^2 gluons are canceled out from the
spectrum, (v) the critical deconfinement temperature is in good agreement with
lattice data. Using the same approximation, we find confinement for the
exceptional gauge group G(2) and a first-order deconfinement transition, also
in agreement with lattice findings.Comment: Invited talk at the Landau Memorial Conference "Advances in
Theoretical Physics", June 22-26, 2008, Chernogolovka, to be published in the
Proceeding
Proximity-induced superconductivity in graphene
We propose a way of making graphene superconductive by putting on it small
superconductive islands which cover a tiny fraction of graphene area. We show
that the critical temperature, T_c, can reach several Kelvins at the
experimentally accessible range of parameters. At low temperatures, T<<T_c, and
zero magnetic field, the density of states is characterized by a small gap
E_g<T_c resulting from the collective proximity effect. Transverse magnetic
field H_g(T) E_g is expected to destroy the spectral gap driving graphene layer
to a kind of a superconductive glass state. Melting of the glass state into a
metal occurs at a higher field H_{g2}(T).Comment: 4 pages, 3 figure
Coherent transport in Josephson-Junction rhombi chain with quenched disorder
We consider a chain of Josephson-junction rhombi (proposed originally by
Doucot and Vidal) in quantum regime. In a regular chain with no disorder in the
maximally frustrated case when magnetic flux through each rhombi \Phi_r is
equal to one half of superconductive flux quantum \Phi_0, Josephson current is
due to correlated transport of pairs of Cooper pairs, i.e. charge is quantized
in units of . Sufficiently strong deviation \delta\Phi =|\Phi_r-\Phi_0/2| >
\delta\Phi^c from the maximally frustrated point brings the system back to
usual -quantized supercurrent. For a regular chain \delta\Phi^c was
calculated by us previously. Here we present detailed analysis of the effect of
quenched disorder (random stray charges and random fluxes piercing rhombi) on
the pairing effect.Comment: 21 pages, 5 figure
Weak Charge Quantization on Superconducting Islands
We consider the Coulomb blockade on a superconductive quantum dot strongly
coupled to a lead through a tunnelling barrier and/or normal diffusive metal.
Andreev transport of the correlated pairs leads to quantum fluctuations of the
charge on the dot. These fluctuations result in exponential renormalization of
the effective charging energy. We employ two complimentary ways to approach the
problem, leading to the coinciding results: the instanton and the functional RG
treatment of the non-linear sigma model. We also derive the charging energy
renormalization in terms of arbitrary transmission matrix of the multi-channel
interface.Comment: 21 pages, 4 eps figures, RevTe
Order and Creep in Flux Lattices and CDWs Pinned by Planar Defects
The influence of randomly distributed point impurities \emph{and} planar
defects on the order and transport in type-II superconductors and related
systems is considered theoretically. For planar defects of identical
orientation the flux line lattice exhibits a new glassy phase dominated by the
planar defects with a finite compressibility, a transverse Meissner effect,
large sample to sample fuctuations of the susceptibility and an exponential
decay of translational long range order. The flux creep resistivity for
currents parallel to the defects is .
Strong disorder enforces an array of dislocations to relax shear strain
Magnus Force in Discrete and Continuous Two-Dimensional Superfluids
Motion of vortices in two-dimensional superfluids in the classical limit is
studied by solving the Gross-Pitaevskii equation numerically on a uniform
lattice. We find that, in the presence of a superflow directed along one of the
main lattice periods, vortices move with the superflow on fine lattices but
perpendicular to it on coarse ones. We interpret this result as a transition
from the full Magnus force in the Galilean-invariant limit to vanishing
effective Magnus force in a discrete system, in agreement with the existing
experiments on vortex motion in Josephson junction arrays.Comment: 6 pages, 7 figures; published in Phys. Rev.
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