Yu. N. Ovchinnikov

Pinning in type II superconductors

Large and randomly arranged pinning centers cause a strong deformation of a flux line lattice, so that each pinning center acts on the lattice with a maximum force. The average force for such single-particle pinning can be inferred from a simple summing procedure and has a domelike dependence on magnetic field. Pinning centers of average force, such as clusters of dislocations, strongly deform the flux line lattice only in weak fields and in fields close to the critical field, where there is a peak in the dependence of the critical current on magnetic field. In the range of intermediate fields there is a weak collective pinning. A large concentration of weak centers leads to collective pinning in all fields. In this case, near the critical field a critical current peak should be observed. To explain this peak and to define the boundaries between the regions of collective and single-particle pinning the possible break-off of the flux line lattice from the lines of magnetic force should be taken into consideration, which leads to extra softening of the lattice.

Number of bound states of three-body systems and Efimov's effect

Abstract Using the variational approach we obtain lower bounds for the number of eigenvalues of three-particle Hamiltonians with short-range potentials close to critical ones and construct corresponding trial functions. A new proof of the infiniteness of the number of eigenvalues for critical potentials (Efimovs effect) is given.

Fluctuation conductivity in the vicinity of the superconducting transition

The conductivity of the metal in the vicinity of the superconductivity transition point has been obtained. The nonlinear fluctuation effects change the temperature dependence of the conductivity in a wide range of temperatures, in which fluctuation corrections to thermodynamic quantities are still small. At comparatively strong pair breaking these effects decrease the fluctuation correction, which may exceed the conductivity of normal metal far from the transition temperature.

Quantum creep of vortices in granular superconductors

Abstract Recent experimental and theoretical studies of granular superconducting systems have attracted great attention. In general, the superconducting grains are only weakly coupled, and therefore at low temperatures the order parameter has a fixed modulus which is independent of any super current flow. It is the phase of the order parameter only which remains a degree of freedom for each grain. In such a case there exist vortex configurations and one expects minima in the potential energy when the center of the vortex is situated in the free space between the grains. We consider here the case where the energy barrier which separates the adjacent minima is sufficiently well developed. Then, a vortex may change its position by thermal activation over the top of the barrier or by quantum tunneling between neighboring minima. In this paper we study this quantum tunneling which, in the presence of a transport current, leads to a creep-like flow of vortices.

The Ginzburg-Landau equation III. Vortex dynamics

In this paper we study the time-dependent Ginzburg-Landau equation of the Schrodinger type in two dimensions. The initial conditions are chosen to describe several well-separated vortices. Our task is to understand the vortex structure of the corresponding solutions as well as corrections due to radiation. To this end we develop the nonlinear adiabatic theory. Using the methods of effective action and of geometric solvability we derive equations for the vortex dynamics and radiation. As an example we consider the special case of radiation by two 1-vortices.

Long-time behaviour of Ginzburg-Landau vortices

In this paper we continue our study of the long-time behaviour of solutions of the non-stationary Ginzburg Landau equation of the Schrodinger type. Here we consider initial conditions corresponding to either two vortices of charges +1 each or two vortices of opposite charges +1 and -1. We show that in the first case the vortices radiate while rotating around each other. As a result of this radiation they move apart at the rate of asymptotically. In the second case we show that the radiation is absent for large vortex separations which conforms with previous results. For separations of orders O (1) and less we argue that the vortex pair produces a shock wave. As a result it loses energy and eventually collapses.

Resonance reduction of the lifetime of the metastable state of tunnel junctions

The lifetime of a metastable current state of a tunnel junction is reduced under the action of a weak microwave perturbation. The dependence of the lifetime on pumping frequency is found and describes the experimental data. At a very highQ-factor, frequent sharp dips appear in the dependence of the lifetime on pumping frequency. These dips are connected with the quantum properties of the phase of the order parameter.

THE KINKED VORTICES IN LAYERED SUPERCONDUCTORS IN THE PRESENCE OF A TILTED MAGNETIC FIELD

In highly layered high-Tc superconductors in the presence of a magnetic field having an angle with respect to the planes, a system of vortex kinks is a more appropriate description of the structure than a set of rectilinear vortices. This description leads to a finite jump of the sample torque at zero angle between planes and magnetic field direction, to the nontrivial behaviour of the ratio at the perpendicular and parallel magnetization, and to strong anisotropy of the critical current.

Collapse of an instanton

We construct a two-parameter family of collapsing solutions to the 4 + 1 Yang–Mills equations and derive the dynamical law of the collapse. Our arguments indicate that this family of solutions is stable. The latter fact is also supported by numerical simulations.

RESISTANCE OF LAYERED SUPERCLEAN SUPERCONDUCTORS AT LOW TEMPERATURES

The low energy excitation spectrum is found for a layered superconductor vortex with a small number of impurities inside the vortex core. All levels are found to be correlated. This leads to the strong enhancement of conductivity in superclean layered superconductors.