Tunneling, relaxation of spin-polarized quasiparticles, and spin-charge separation in superconductors

The nonequilibrium spin imbalance created when electrons tunnel from a ferromagnet to a superconductor is calculated. Since the charge current in a superconductor is carried by the condensate within a penetration length of the surface and the spin current, which is carried by quasiparticles, can exist in the bulk, one may be able to directly demonstrate spin-charge separation in a superconductor using spin injection techniques. After estimating the spin-relaxation rates due to magnetic impurity and spin-orbit scattering, an explicit experimental geometry for demonstration of spin-charge separation is discussed.