161,681 research outputs found
Strong vortex-antivortex fluctuations in the type II superconducting film
The small size vortex-antivortex pairs proliferation in type II
superconducting film is considered for the wide interval of temperatures below
Tc. The corresponding contribution to free energy is calculated. It is shown
that these fluctuations give the main contribution to the heat capacity of the
film both at low temperatures and in the vicinity of transition
On the number of two-dimensional threshold functions
A two-dimensional threshold function of k-valued logic can be viewed as
coloring of the points of a k x k square lattice into two colors such that
there exists a straight line separating points of different colors. For the
number of such functions only asymptotic bounds are known. We give an exact
formula for the number of two-dimensional threshold functions and derive more
accurate asymptotics.Comment: 17 pages, 2 figure
How the Phase Slips in a Current-Biased Narrow Superconducting Stripe?
The theory of current transport in a narrow superconducting channel
accounting for thermal fluctuations is revisited. The value of voltage
appearing in the sample is found as the function of temperature (close to
transition temperature ) and bias
current ( is a value of critical current
calculated in the framework of the BCS approximation, neglecting thermal
fluctuations). It is shown that the careful analysis of vortex crossing of the
stripe results in considerable increase of the activation energy.Comment: 6 pages, 2 figure
Describing neutrino oscillations in matter with Magnus expansion
We present new formalism for description of the neutrino oscillations in
matter with varying density. The formalism is based on the Magnus expansion and
has a virtue that the unitarity of the S-matrix is maintained in each order of
perturbation theory. We show that the Magnus expansion provides better
convergence of series: the restoration of unitarity leads to smaller deviations
from the exact results especially in the regions of large transition
probabilities. Various expansions are obtained depending on a basis of neutrino
states and a way one splits the Hamiltonian into the self-commuting and
non-commuting parts. In particular, we develop the Magnus expansion for the
adiabatic perturbation theory which gives the best approximation. We apply the
formalism to the neutrino oscillations in matter of the Earth and show that for
the solar oscillation parameters the second order Magnus adiabatic expansion
has better than 1% accuracy for all energies and trajectories. For the
atmospheric and small 1-3 mixing the approximation works well ( accuracy for ) outside the resonance region
(2.7 - 8) GeV.Comment: Discussions expanded, two figures and references added, the version
will appear in Nucl. Phys.
Phase-sensitive quantum effects in Andreev conductance of the SNS system of metals with macroscopic phase breaking length
The dissipative component of electron transport through the doubly connected
SNS Andreev interferometer indium (S)-aluminium (N)-indium (S) has been
studied. Within helium temperature range, the conductance of the individual
sections of the interferometer exhibits phase-sensitive oscillations of
quantum-interference nature. In the non-domain (normal) state of indium
narrowing adjacent to NS interface, the nonresonance oscillations have been
observed, with the period inversely proportional to the area of the
interferometer orifice. In the domain intermediate state of the narrowing, the
magneto-temperature resistive oscillations appeared, with the period determined
by the coherence length in the magnetic field equal to the critical one. The
oscillating component of resonance form has been observed in the conductance of
the macroscopic N-aluminium part of the system. The phase of the oscillations
appears to be shifted by compared to that of nonresonance oscillations.
We offer an explanation in terms of the contribution into Josephson current
from the coherent quasiparticles with energies of order of the Thouless energy.
The behavior of dissipative transport with temperature has been studied in a
clean normal metal in the vicinity of a single point NS contact.Comment: 9 pages, 7 figures, to be published in Low Temp. Phys., v. 29, No.
12, 200
Josephson and spontaneous currents at the interface between two d-wave superconductors with transport current in the banks
A stationary Josephson effect in the ballistic contact of two d-wave
superconductors with different axes orientation and with tangential transport
current in the banks is considered theoretically. We study the influence of the
transport current on the current-phase dependence for the Josephson and
tangential currents at the interface. It is demonstrated that the spontaneous
surface current at the interface depends on the transport current in the banks
due to the interference of the angle-dependent current-carrying condensate wave
functions of the two superconductors.Comment: to be published in Fiz. Nizk. Temp. (Sov. J. Low Temp. Phys.),
Vol.30, No.3 (2004
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