Superconductor spintronics: modeling spin and charge accumulation in out-of-equilibrium NIS junctions subjected to Zeeman magnetic fields

We study the spin and charge accumulation in a superconductor when a normal-superconductor tunnel junction is subjected to a Zeemanmagnetic field and taken out of equilibrium by applying either aDCor AC voltage bias. Wefocus on a configuration which allows one to measure non-locally the spin-accumulation using a second ferromagnetic electrode. Ourmain result is that, in the presence of an AC bias, the time average of the detected non-local signal is frequency dependent, and the frequency at which the saturation occurs is directly related to the inverse of the spin-relaxation time. For a DC bias we also address the effect of the spin accumulation in the normal leads and we investigate the out-of-equilibrium spin susceptibility of the SC, whichwe show to deviate drastically from its equilibrium value.