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 $T-T_{\mathrm{c}}$ $\ll T_{\mathrm{c}}$) and bias current $J<J_{\mathrm{c}}$ ( $J_{\mathrm{c}}$ 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 $V(\rho)$. 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 $V(\rho)$ 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 $\rho^2/R^2$ and $R/a_B^*$ ($R$ is the dot radius and $a_B^*$ 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 $\chi$ and to the specific heat $C$ of a metal. The impurity contribution to the magnetic susceptibility has a $1/T^2$ behaviour, and the impurity contribution to the specific heat has a $1/T$ behaviour, both in an extended region of temperatures $T$. 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 $C$ and $\chi$ 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 $T >0$. 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 $T$ converges to an equilibrium state of the coupled system at the same temperature, as time tends to $+ \infty

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 $\mu H\sim 0.5 T_c$ ($T_c$ is the Kondo temperature) there is an inflection point, and in the strong magnetic field range $\mu H\gg T_c$, the correction to the average spin is proportional to $(T_c/\mu H)^2$. In zero magnetic field, the interaction with conduction electrons also leads to the splitting of doubly degenerate spin impurity states

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