Quasiparticle-mediated spin Hall effect in a superconductor

In some materials the competition between superconductivity and magnetism brings about a variety of unique phenomena such as the coexistence of superconductivity and magnetism in heavy-fermion superconductors(1) or spin-triplet supercurrent in ferromagnetic Josephson junctions(2-4). Recent observations of spin-charge separation in a lateral spin valve with a superconductor(5,6) evidence that these remarkable properties are applicable to spintronics(7), although there are still fewworks exploring this possibility. Here, we report the experimental observation of the quasiparticle-mediated spin Hall effect in a superconductor, NbN. This compound exhibits the inverse spin Hall (ISH) effect(8) even below the superconducting transition temperature. Surprisingly, the ISH signal increases by more than 2,000 times compared with that in the normal state with a decrease of the injected spin current. The effect disappears when the distance between the voltage probes becomes larger than the charge imbalance length(9,10), corroborating that the huge ISH signals measured are mediated by quasiparticles.