Magnon-assisted Andreev transport across ferromagnet–superconductor junctions

We study subgap transport due to Andreev reflection in a ferromagnet–superconductor junction at low temperature. The mismatch of spin polarized current in the ferromagnet and spinless current in the superconductor results in an additional contact resistance which can be reduced by magnon emission in the ferromagnet. We find that magnon-assisted Andreev reflection produces a non-linear contribution to the asymmetric part of the conductance, G(V)−G(−V), which is related to the density of states of magnons in the ferromagnet.