A. I. Larkin

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.

The influence of fluctuation pairing of electrons on the conductivity of normal metal

Abstract The theoretical consideration of the influence of the fluctuation pairing on the conductivity of a normal film leads to the law: σ = σ res + e 2 (T−T c ) 16 d h T c in good agreement with experimental data.

Pinning and creep in layered superconductors

Abstract The thermal- and disorder-induced effects in the mixed state of a layered high- T c superconductor (in a field H ‖ c ) are studied. The flux line lattice is of a quasi-2D type at sufficiently high field H ⪆ H 0 where H 0 is proportional to the mass anisotropy m / M and estimated to be around 3 T for the Bi- and Tl-based superconductors. At H 》 H 0 the FLL melts at a temperature T m close to the temperature of 2D dislocation-mediated melting. At T > T m the system is in the normal state. At low temperatures T T g ⋍ T m / In ( H / H 0 ) the system is in the vortex glass state with zero linear resistivity: ∂ V /∂ j →0 as j →0. In the intermediate temperature range T g T T m the energy barriers for the plastic motion of vortices are finite and thermally activated flux flow (TAFF) occurs. In the vortex glass state, different regimes of flux pinning and creep are identified and the behaviour of the critical current j c as a function of temperature and magnetic field is estimated. Power-law behaviour of the effective pinning energy U ( j ) at j ⪌ j c is obtained for the case of 2D collective creep.

Magnetoresistance of high temperature superconductors

Magnetoresistance for high temperature superconductors is investigated above the critical point. Near transition temperature, there is a crossover from two dimensions to three dimensions. According to superconducting fluctuation, a crossover between different contributions of magnetoresistance appears. The phase relaxation time and the theoretical formula of the crossover in the magnetoresistance are discussed.

Superconductivity in a system with preformed pairs

We discuss the phenomenology of superconductivity resulting from the Bose condensation of preformed pairs coexisting with unpaired fermions. We show that this transition is more mean-field-like than the usual Bose condensation, i.e., it is characterized by a relatively small value of the Ginzburg parameter. We consider the Hall effect in the vortex-flow regime and in the fluctuational regime above

Persistent current in superconducting nanorings

{\mathrm{T}}_{\mathrm{c}}

Flux pinning and creep in high-Tc superconductors

, and show that in this situation it is much less than in the transition driven entirely by Bose condensation but much larger than in usual superconductivity. We analyze the available Hall data and conclude that this phenomenology describes reasonably well the data in the underdoped materials of Y-Ba-Cu-O family but is not an appropriate description of optimally doped materials or underdoped La-Sr-Cu-O.

Divergence of classical trajectories and weak localization.

The superconductivity in very thin rings is suppressed by quantum phase slips. As a result, the amplitude of the persistent current oscillations with flux becomes exponentially small, and their shape changes from sawtooth to a sinusoidal one. We reduce the problem of low-energy properties of a superconducting nanoring to that of a quantum particle in a sinusoidal potential and show that the dependence of the current on the flux belongs to a one-parameter family of functions obtained by solving the respective Schrödinger equation with twisted boundary conditions.

Nature of the Irreversibility Line in Bi2Sr2CaCu2O8

Abstract The theory of collective pinning in the presence of thermal fluctuations of vortex lines is developed. Critical current jc is shown to decrease rapidly with temperature. Flux creep under the action of weak (j

Parity Effect in Ground State Energies of Ultrasmall Superconducting Grains

We study the weak localization correction (WLC) to transport coefficients of a system of electrons in a static long-range potential (e.g. an antidot array or ballistic cavity). We found that the weak localization correction to the current response is delayed by the large time