Yu.M. Ivanchenko

Nonlocal interaction in Josephson junctions

Abstract The electrodynamics of Josephson junctions in thin superconducting films has been investigated. It is shown that the electro- dynamic equation for the phase difference is essentially nonlocal. The solution of Josephson vortex type is analyzed.

New small RG parameter

Abstract The exact functional renormalization group (RG) equation is used to construct a new version of the perturbation theory whose small parameter is the Fisher exponent η.

Critical behavior and finite volume

An exactly solvable model is used to investigate the influence of the finite size of a system on its critical behavior. The renormalization of the critical temperature is calculated together with the critical exponents and the correlation function. A crossover of the critical exponents from their scaling values to the exponents of mean field theory is obtained. The possibility of complete disappearance of the region of scaling under the influence of the finite size of the system is demonstrated.

Squeezed vortex in a layered structure of type-II superconductors

Abstract London approximation is used to solve the problem of magnetic vortex destroying order parameter in a superconducting layer of arbitrary thickness embedded between bulk superconducting screens. Like the well-known 2D-vortices in layered superconductors, the vortices under consideration interact logarithmically at large distances and carry magnetic flux θ θ 0 , the unit flux quantum. The stability of long vortices in a layered superconductor is discussed with respect to the decay of shorter vortices.

Surface logarithmic correlations in BiSrCaCuO single crystals

Abstract Low temperature STM techniques are applied to study statistical properties of the BiO plane in 2212 high- T c single crystals. The correlation functions of height deviations in x and k spaces have been numerically obtained. Long range power law correlations have been found and attributed to half lattice cell jumps of known height in the c direction. Theoretical analysis of the correlation function resulting, from the assumption that the jumps on the surface are formed by two oppositely charged partial screw dislocations, gives very good agreement with the experimentally found behavior.

Fluctuation-induced phase transition of the first kind in an exactly solvable model

A system with cubic anisotropy of the vertices of fourth order is investigated in the framework of a model that admits exact calculation of the partition function. It is shown that for a definite relationship between the parameters of the free energy functional the phase transition in such a system becomes abrupt, whereas mean field theory predicts a phase transition of the second kind under the same conditions. The result agrees with the analogous predictions of fluctuation theory.

Vortex ring excitations in layered superconductors

Abstract A special kind of thermal excitations can be found in the vicinity of T c in a layered superconducting structure. The excitations are vortex rings positioned in the layer with weaker superconductivity. For parameters corresponding to high- T c superconductors these excitations should consist of two coupled vortex rings with opposite helicities. Fixed in position by pinning forces and frozen, these excitations contribute to randomization of the superconducting state at low temperatures. Estimates are made for the density of states within the gap region and characteristic length of the random structure caused by the double ring excitations.

Critical behaviour of orthorhombic high Tc superconducting systems with d-pairing

Abstract The prediction of possible superconductivity transition splitting in orthorhombic high T c superconducting systems based on the Landau theory is tested by the renormalization group technique. It is shown that at small orthorhombicity Δ this splitting is absent and appears only at some Δ min .

Noise anomalies in small tunnel junctions at low temperatures

Abstract The discreteness of the carriers energy spectrum in small tunnel junctions is shown to cause the anomalous dependence of noise power on temperature S (ω)∼ T -1 at low temperatures instead of the proportionality predicted by the Nyquist formula. The effect manifest itself in the second order of the expansion in powers of the tunnel barrier transparency.

Exact calculation of the current in the tunnel Hamiltonian method

A method is proposed for going over from the nonequilibrium formulation to the thermal Greens function technique in the tunnel model. The method is used to obtain an exact solution for the current and the radius of convergence of the series of perturbation theory with respect to the transparency. The divergence of the series is found to be related to the rearrangement of the spectrum in sufficiently transparent tunnel junctions.