Thermal responses of spin density and spin current induced by Bogoliubov Fermi surfaces in proximity superconductors

The emergence of Bogoliubov Fermi surfaces in s-wave proximity superconducting systems provides a unique platform for generating nontrivial spin responses in the presence of spin-orbit coupling. In this work, we investigate temperature-gradient driven responses of spin polarization and spin current in such a proximity system related to Fe(Te,Se). The interplay of in-plane magnetization, superconductivity, and nematicity gives rise to nontrivial Berry curvature and spin-related hybrid Berry curvature on the Bogoliubov Fermi surfaces, which are shown to lead to finite thermally driven nonequilibrium spin polarization and spin Nernst effect. We find that the responses are strongly enhanced by the emergence of Bogoliubov Fermi surfaces, and are linear in temperature at low temperatures, rendering a unique spintronic character of Bogoliubov Fermi surfaces.