Thermal, electric and spin transport in superconductor/ferromagnetic-insulator structures

Abstract

A ferromagnetic insulator (FI) attached to a conventional superconductor (S) changes drastically the properties of the latter. Specifically, the exchange field at the FI/S interface leads to a splitting of the superconducting density of states. If S is a superconducting film, thinner than the superconducting coherence length, the modification of the density of states occurs over the whole sample. The coexistence of the exchange splitting and superconducting correlations in S/FI structures leads to striking transport phenomena that are of interest for applications in thermoelectricity, superconducting spintronics and radiation sensors. Here we review the most recent progress in understanding the transport properties of FI/S structures by presenting a complete theoretical framework based on the quasiclassical kinetic equations. We discuss the coupling between the electronic degrees of freedom, charge, spin and energy, under non-equilibrium conditions and its manifestation in thermoelectricity and spin-dependent transport.

Quasiclassical free energy of superconductors: Disorder-driven first-order phase transition in superconductor/ferromagnetic-insulator bilayers

“…is given by the selfconsistency relation for the gap function, which is a linear functional that describes all possible types of pairings. In addition, there are other contributions to , e.g., from various scattering mechanisms, including potential impurity scattering, spin-orbital, and spin-flip relaxations [20].…”

“…The λ integral in (3) can be evaluated using an approach suggested in Ref. [20]. Let us note the general relation,…”

“…The saddle point of this expression yields the Usadel equation [3] forĝ s and the self-consistency equation forˆ , and, therefore, (20) is naturally considered as the free-energy candidate.…”

Spin and charge currents driven by the Higgs mode in high-field superconductors

“…Here we suggest a different mechanism allowing electrical detection of HMs due to their coupling with spin and charge degrees of freedom in high-field superconductor/ferromagnet junctions. Unusual transport properties of such systems have attracted intense attention [34][35][36][37], stimulating both experimental [38][39][40][41][42][43][44][45][46][47] and theoretical efforts [34,[48][49][50][51][52][53][54][55][56][57].…”

Nonlinear spin torque, pumping, and cooling in superconductor/ferromagnet systems

“…Recently there has also been increased interest to couple superconductors to magnets and find out how superconductivity affects the magnetization dynamics, [5][6][7][8][9][10][11][12][13][14][15] including thermally driven effects [16]. On the other hand, recent work has shown that a combination of magnetic and superconducting systems results to giant thermoelectric effects [17][18][19][20] coupling charge and heat currents. These works [18] also imply the coupling spin and heat.…”