Unusual Sequence of the Critical Magnetic Fields Hc1, Hc2, and Hc in Multicomponent Superconductors.

All superconductors in a magnetic field are characterized by three critical magnetic fields: lower critical Hc1, upper critical Hc2 and thermodynamic critical field Hc. Only two sets of inequalities Hc2>Hc>Hc1 or Hc1>Hc>Hc2 are possible in a single-component superconductor. Here, we report our study of the critical fields in multicomponent superconductors with two superconducting components in the framework of the Ginzburg-Landau functional. We derive the relationship between the phases of the components of the superconducting complex order parameter from the charge conservation law in explicit form and insert it into the Ginzburg-Landau functional. Using the modified Ginzburg-Landau equation, we acquire the single vortex state including the analytical expression for asymptotics. Also, we obtain the analytical form for the state in the upper critical field. We find that in some cases an unusual sequence of critical fields Hc1,Hc2>Hc can be realized in multicomponent superconductors.

Macroscopic quantum tunneling in "small" Josephson junctions in a magnetic field.

We study the phenomenon of macroscopic quantum tunneling (MQT) in small Josephson junctions (JJ) with an externally applied magnetic field. The latter results in the appearance of the Fraunhofer type modulation of the current density along the barrier. The problem of MQT for a pointlike JJ is reduced to the motion of the quantum particle in the washboard potential. In the case of a finite size JJ under consideration, this problem corresponds to a MQT in a potential which itself, besides the phase, depends on space variables. The general expression for the crossover temperature T0 between thermally activated and macroscopic quantum tunneling regimes and the escaping time tau(esc) have been calculated.

Effect of vortex-antivortex fluctuations on the heat capacity of a type-II superconducting film.

The small size vortex-antivortex pairs proliferation in a type-II superconducting film is considered below T(c). The corresponding contribution to the free energy is calculated. It is shown that these fluctuations give the main temperature dependent contribution to the heat capacity of the superconducting film in the sufficiently large interval of temperatures below the transition point.