Colloquium: Nonequilibrium effects in superconductors with a spin-splitting field

This Colloquium discusses the recent progress in understanding the properties of spin-split superconductors under nonequilibrium conditions. Recent experiments and theories demonstrate a rich variety of transport phenomena occurring in devices based on such materials that suggest direct applications in thermoelectricity, low-dissipative spintronics, radiation detection, and sensing. This text discusses different experimental situations and presents a theoretical framework based on quantum kinetic equations. This framework provides an accurate description of the nonequilibrium distribution of charge, spin, and energy, which are the relevant nonequilibrium modes, in different hybrid structures. This Colloquium also reviews experiments on spin-split superconductors and shows how transport measurements reveal the properties of the nonequilibrium modes and their mutual coupling. In particular, the emphasis of the text is on spin injection and diffusion and very large thermoelectric effects in spin-split superconductors.This work was supported by the Academy of Finland Center of Excellence (Project No. 284594), Research Fellow (Project No. 297439), and Key Funding (Project No. 305256) programs, the Spanish Ministerio de Economía y Competitividad (MINECO, Project No. FIS2014-55987-P), the Spanish Ministerio de Ciencia, Innovación y Universidades (MICINN, Project No. FIS2017-82804-P), and the European Research Council under the European Union’s Seventh Framework Program (FP7/2007-2013)/ERC Grant agreements No. 240362-HEATTRONICS and No. 615187-COMANCHE.Peer Reviewe