On-demand thermoelectric generation of equal-spin Cooper pairs

A central goal for the application of superconductors in spintronics is the on-demand generation of spin-polarized supercurrents or, analogously, of equal-spin Cooper pairs. Most proposals rely on a careful manipulation of magnetic materials to electrically generate equal-spin Cooper pairs in ferromagnet (F)-superconductor (S) hybrid junctions. Here, we propose a quantum heat engine that utilizes the helicity of the edge states of a quantum spin Hall insulator instead, where nonlocal transport necessarily takes place through equal-spin channels. We demonstrate that a temperature bias applied to an S-F-S junction can drive a nonlocal polarized supercurrent, while the normal contribution from electron tunneling is suppressed. Remarkably, the relative phase between the superconductors serves as a switch to turn the thermoelectric current on and off, allowing for the creation of equal-spin Cooper pairs on demand.