650 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
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
Flat Thomas-Fermi artificial atoms
We consider two-dimensional (2D) "artificial atoms" confined by an axially
symmetric potential . Such configurations arise in circular quantum
dots and other systems effectively restricted to a 2D layer. Using the
semiclassical method, we present the first fully self-consistent and analytic
solution yielding equations describing the density distribution, energy, and
other quantities for any form of and an arbitrary number of confined
particles. An essential and nontrivial aspect of the problem is that the 2D
density of states must be properly combined with 3D electrostatics. The
solution turns out to have a universal form, with scaling parameters
and ( is the dot radius and is the effective
Bohr radius)
Nuclear magnetic susceptibility of metals with magnetic impurities
We consider the contribution of magnetic impurities to the nuclear magnetic
susceptibility and to the specific heat of a metal. The impurity
contribution to the magnetic susceptibility has a behaviour, and the
impurity contribution to the specific heat has a behaviour, both in an
extended region of temperatures . In the case of a dirty metal the RKKY
interaction of nuclear spins and impurity spins is suppressed for low
temperatures and the main contribution to and is given by their
dipole-dipole interaction.Comment: 9 pages, 4 figures, REVTE
Non-radially symmetric solutions to the Ginzburg-Landau equation
We study an atom with finitely many energy levels in contact with a heat bath consisting of photons (black body radiation) at a temperature . The dynamics of this system is described by a Liouville operator, or thermal Hamiltonian, which is the sum of an atomic Liouville operator, of a Liouville operator describing the dynamics of a free, massless Bose field, and a local operator describing the interactions between the atom and the heat bath. We show that an arbitrary initial state which is normal with respect to the equilibrium state of the uncoupled system at temperature converges to an equilibrium state of the coupled system at the same temperature, as time tends to $+ \infty
On collapse of wave maps
We derive the universal collapse law of degree 1 equivariant wave maps
(solutions of the sigma-model) from the 2+1 Minkowski space-time,to the
2-sphere. To this end we introduce a nonlinear transformation from original
variables to blowup ones. Our formal derivations are confirmed by numerical
simulations.Comment: 1 figur
Strong coupling in the Kondo problem in the low-temperature region
The magnetic field dependence of the average spin of a localized electron
coupled to conduction electrons with an antiferromagnetic exchange interaction
is found for the ground state. In the magnetic field range
( is the Kondo temperature) there is an inflection point, and in the
strong magnetic field range , the correction to the average spin
is proportional to . In zero magnetic field, the interaction
with conduction electrons also leads to the splitting of doubly degenerate spin
impurity states
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