Correlated tunneling into a superconductor in a multiprobe hybrid structure

We consider tunneling in a hybrid system consisting of a superconductor wit h two or more probe electrodes which can be either normal metals or polariz ed ferromagnets. In particular we study transport at subgap voltages and te mperatures. Besides Andreev pair tunneling at each contact, in multi-probe structures subgap transport involves additional channels, which are due to coherent propagation of two particles (electrons or holes), each originatin g from a different probe electrode. The relevant processes are electron cot unneling through the superconductor and conversion into a Cooper pair of tw o electrons stemming from different probes. These processes are non-local a nd decay when the distance between the pair of involved contacts is larger than the superconducting coherence length. The conductance matrix of a thre e-terminal hybrid structure is calculated. The multi-probe processes enhanc e the conductance of each contact. If the contacts are magnetically polariz ed the contribution of the various conduction channels can be separately de tected.