I.B. Khalfin

Relaxation of magnetic flux in a superconductor with a system of columnar defects

Abstract The interaction of Abrikosov vortices with columnar defects (with single defects and with a periodical structure) is considered. It is shown that interdefect regions can play the role of pinning centers because of the existence of a potential barrier for vortices. The energy barrier and the magnetic relaxation rate as a function of temperature are calculated. A step-like behavior of the magnetic relaxation rate in a high magnetic field is predicted.

The electric field action on high-Tc superconductors

Abstract The theory of the surface superconductivity induced by the static electric field perpendicular to the thin film is presented. The shift of the critical temperature and the behavior of paraconductivity as functions of the film thickness are calculated.

On the onset of stochastic resonance

Abstract All three essential ingredients (nonlinearity, periodic and random forces) are necessary for the onset of stochastic resonance. The mobility of an overdamped particle moving in a periodic potential and subject to a stochastic and a constant force (rather than a periodic one) remains a monotonic function of noise intensity in contrast to the results of Gang Hu [Phys. Lett. A 174 (1993) 247].

Charged grain boundaries as pinning centers in high-Tc superconductors

Abstract The theory of the Abrikosov vortex pinning by charged grain boundaries in high-temperature superconductors is presented. We show that due to the small ratio ζ/ l D inhigh-temperature superconductors (where ζ is the coherence length and l D is the Debve screening length) the attraction of the Abrikosov vortices to the grain boundary is significantly greater than in conventional superconductors.

Critical current in high-Tc superconductors in external electric field

Abstract An electric field directed perpendicular to the surface of a superconductor changes the superconducting properties near the surface and creates an additional barrier for flux penetration into the sample. This effect is characterized by the value l D / ξ , where l D is the Debye screening length and ξ is the coherence length, and can be neglected in conventional superconductors with l D ⪡ ξ . However, in high-temperature superconductors, where l D / ξ ∼1, the effect is very pronounced and could be used for improvement of the transport critical current.

Flux strings in a layered superconductor

Abstract We consider the magnetic flux distribution in a layered superconductor (superlattice) in the magnetic field parallel to the layers. The existance of multivortex states in the form of strings stretched across the layers is predicted. These states can change dramatically both the processes of magnetization and of the magnetic relaxation of the layered superconductor.

Superconducting thin films in a static electric field

Abstract A theory of the surface superconductivity induced by a static electric field perpendicular to a thin film is presented. The shift of the critical temperature and the higher magnetic field of the superconducting transition as functions of the film thickness are calculated.

Multivortex states in large pinning centers

We have studied the vortex pinning in the large centers, i.e. in the spatial regions with the characteristic size a comparable with the London lenght λ. It is shown that the type of configuration and the number of vortices in the cluster are dependent on the ration a/λ and change nonmonotonically with the temperature. The influence of such vortex clusters on the decay of magnetization and the current-voltage characteristics are discussed. The important role of the potential barrier for the penetration of vortices into the pinning center is shown. The new state of vortex cluster, “vortex polaron”, is predicted. The stability of the multivortex state is discussed.

Random-signal interaction with flowing lattice of Abrikosov vortices

Abstract The interaction of a random-noise signal with a flowing lattice of Abrikosov vortices leads to strong modifications of the original noise spectrum. The detailed shape of the spectrum depends on the lattice-flow velocity. At low velocities of the lattice flow the spectrum is attenuated at low frequencies similarly to the case of a motionless lattice. For the velocities above the crossover velocity the spectrum magnitude oscillates with a characteristic frequency depending on the time of flight of the vortices across the strip dimension perpendicular to the direction of current flow. For sufficiently high magnetic fields the bias current determining the crossover to the oscillatory regime depends only on the temperature and film thickness.

Magnetic flux in a layered superconductor with trapped chains of fluxons

Abstract We consider the magnetic flux distribution in a layered superconductor (superlattice) in the magnetic field parallel to the layers. The existance of multivortex states in the form of strings with pinned edges stretched across the layers is predicted. These states can change dramatically both the processes of magnetization and of the magnetic relaxation of the layered superconductor.