0000000000016613
AUTHOR
Artjom Vargunin
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…
Self-consistent calculation of the flux-flow conductivity in diffusive superconductors
In the framework of Keldysh-Usadel kinetic theory, we study the temperature dependence of flux-flow conductivity (FFC) in diffusive superconductors. By using self-consistent vortex solutions we find the exact values of dimensionless parameters that determine the diffusion-controlled FFC both in the limit of the low temperatures and close to the critical one. Taking into account the electron-phonon scattering we study the transition between flux-flow regimes controlled either by the diffusion or the inelastic relaxation of non-equilibrium quasiparticles. We demonstrate that the inelastic electron-phonon relaxation leads to the strong suppression of FFC as compared to the previous estimates m…
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 $\pi$ 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 value of the exchange energy in the ferromagnet. We also show that the $0$-$\pi$ transitions in the perpendicular field can be observed as the specific features of the flux-flow conducti…
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.
Flux flow spin Hall effect in type-II superconductors with spin-splitting field
We predict the very large spin Hall effect in type-II superconductors which mechanism is drastically different from the previously known ones. We find that in the flux-flow regime the spin is transported by the spin-polarized Abrikosov vortices moving under the action of the Lorenz force in the direction perpendicular to the applied electric current. Due to the large vortex velocities the spin Hall angle can be of the order of unity in realistic systems based on the high-field superconductors or the recently developed superconductor/ferromagnetic insulator proximity structures. We propose the realization of high-frequency pure spin current generator based on the periodic structure of moving…
Quasiclassical expressions for the free energy of superconducting systems
In the seminal work by G. Eilenberger [Z. Phys. 214, 195 (1968)], the quasiclassical expression for the free energy of spin-singlet superconductor has been suggested. Starting from the Luttinger-Ward formulation we derive the Eilenberger free energy and find its generalization for superconductor or superfluid with spin-triplet correlations. Besides ordinary superconductors with various scattering mechanisms, the obtained free energy functional can be used for systems with spin-triplet pairing such as superfluid $^3$He and superconducting systems with spatially-inhomogeneous exchange field or spin-orbit coupling. Using this general result we derive the simplified expression for the free ener…
Quasiclassical free energy of superconductors : Disorder-driven first-order phase transition in superconductor/ferromagnetic-insulator bilayers
In the seminal work by G. Eilenberger, Z. Phys. 214, 195 (1968), a closed-form expression for the free energy of inhomogeneous spin-singlet superconductor in terms of quasiclassical propagators has been suggested. However, deriving this expression and generalizing it for superconductors or superfluids with general matrix structure, e.g., spin-triplet correlations, has remained problematic. Starting from the Luttinger-Ward formulation, we discuss here the general solution. Besides ordinary superconductors with various scattering mechanisms, the obtained free-energy functional can be used for systems, such as superfluid $^{3}\mathrm{He}$ and superconducting systems with spatially inhomogeneou…