Field dependence of the vortex-core sizes in dirty two-band superconductors

We study the structure of Abrikosov vortices in two-band superconductors for different external magnetic fields and different parameters of the bands. The vortex core size determined by the coherence lengths are found to have qualitatively different behaviour from that determined by the quasiparticle density of states spatial variation. These different vortex core length scales coincide near the upper critical field, while the discrepancy between them becomes quite significant at lower fields. Within the diffusive approximation we demonstrate several generic regimes in the field dependence of the vortex core sizes determined by the disparity of diffusion constants in the two bands.Comment: 6 pages, 5 figure

Coherence lengths for superconductivity in the two-orbital negative-U Hubbard model

We study the peculiarities of coherency in the superconductivity of two-orbital system. The superconducting phase transition is caused here by the on-site intra-orbital attractions (negative-U Hubbard model) and inter-orbital pair-transfer interaction. The dependencies of critical and noncritical correlation lengths on interaction channels and band fillings are analyzed.Comment: 5 pages, 3 figures, Acta Physica Polonica (2012) in pres

Critical and non-critical coherence lengths in a two-band superconductor

We study the peculiarities of coherency in a two-gap superconductor. The both intraband couplings, inducing superconductivity in the independent bands, and interband pair-transfer interaction have been taken into account. On the basis of the Ginzburg-Landau equations derived from the Bogoliubov-de Gennes equations and the relevant self-consistency conditions for a two-gap system, we find critical and non-critical coherence lengths in the spatial behaviour of the fluctuations of order parameters. The character of the temperature dependencies of these length scales is determined by the relative contributions from intra- and interband interaction channels.Comment: Accepted for publication in Journal of Superconductivity and Novel Magnetis

Magnetic field-controlled 0−π transitions and their experimental signatures in superconductor-ferromagnet-superconductor junctions

Superconductor-ferromagnet-superconductor Josephson junctions are known to exist in the 0 and π states with the transitions between them controlled by the temperature and ferromagnetic interlayer thickness. We demonstrate that these transitions can be controlled also by the external magnetic field directed perpendicular to the layers. By varying the ratio of diffusion coefficients in superconducting and ferromagnetic layers, these field-controlled transitions can be made detectable for arbitrary large values of the exchange energy in the ferromagnet. We also show that the 0−π transitions in the perpendicular field can be observed as the specific features of the flux-flow conductivity dependencies on the ferromagnetic thickness in accordance with recent experimental results.peerReviewe

Unusual resistive states of multiband superconductors in the effective field theory approach

Starting from the microscopic approach based on multiband Keldysh-Usadel kinetic theory we derive the minimal field-theoretical model equivalent to the time-dependent Ginzburg-Landau theory. We discuss the properties of resistive states determined by the ratio of electric field relaxation length to the superconducting coherence length. In contrast to the well-studied single-band systems we find that this ratio can vary in wide limits in multiband superconductors. As a result, the properties of resistive states in multiband superconductors can be tuned by the microscopic parameters such as the ratio of diffusion coefficients and pairing constants in different bands. As an example we consider moving Abrikosov vortices in two-band superconductor and show that the flux-flow magneto-resistance can strongly deviate from the single-component Bardeen-Stephen estimation in agreement with recent experimental results