Tero Heikkilä
In this tutorial I will describe how the proximity to magnets affects the nonequilibrium properties of superconductors [1,2]. I will in particular emphasize the peculiar superconducting state hosting a spin-splitting field that can be induced into thin superconducting films via in-plane magnetic fields or by their proximity to ferromagnets. Moderate spin splitting does not destroy superconductivity, but results in the presence of an odd-frequency pairing state that also affects the transport properties of the superconductor in a fundamental manner. These transport properties can be studied via tunnelling experiments. In case of local measurements, the spin splitting shows up as a giant thermoelectric effect, whereas the non-local case demonstrates a coupling of the different nonequilibrium modes in the superconductor. The thermoelectric effect can be used for example in new types of superconducting detectors [3]. The dynamic features of the superconducting state are also strongly modified by the spin-splitting field. If the time allows, I will exemplify this via the examples of thermoelectric torques and spin cooling [4], and of the dynamic coupling of magnetization precession and the Higgs amplitude mode in superconductors [5].
[1] F.S. Bergeret, M. Silaev, P. Virtanen, and T.T. Heikkilä, Rev. Mod. Phys. 90, 041001 (2018)[2] T.T. Heikkilä, M. Silaev, P. Virtanen, and F.S. Bergeret, Prog. Surf. Sci. 94, 100540 (2019)
[3] T.T. Heikkilä, R. Ojajärvi, I.J. Maasilta, E. Strambini, F. Giazotto, and F. Bergeret, Phys. Rev. Applied 10, 034053 (2018)
[4] R. Ojajärvi, J. Manninen, T.T. Heikkilä, and P. Virtanen, Phys. Rev. B 101, 115406 (2020)
[5] M. Silaev, R. Ojajärvi, and T.T. Heikkilä, Phys. Rev. Research 2, 033416 (2020)