Superconductivity-enhanced spin pumping: The role of Andreev resonances

We describe a simple hybrid superconductor/ferromagnetic-insulator structure manifesting spin-resolved Andreev bound states in which dynamic magnetization is employed to probe spin related physics. We show that, at low bias and below T_c, the transfer of spin angular momentum pumped by an externally driven ferromagnetic insulator is greatly affected by
the formation of spin-resolved Andreev bound states. For finite thicknesses of the superconducting layer, comparable to the coherence
length, resonant Andreev bound states render highly transmitting subgap spin transport channels. The resonant enhancement of the subgap transport channels establishes a prototype Fabry-Perot resonator for spin pumping.