Correlated tunneling into a superconductor in a multiprobe hybrid structure

Abstract

We consider tunneling in a hybrid system consisting of a superconductor with\ntwo or more probe electrodes which can be either normal metals or polarized\nferromagnets. In particular we study transport at subgap voltages and\ntemperatures. Besides Andreev pair tunneling at each contact, in multi-probe\nstructures subgap transport involves additional channels, which are due to\ncoherent propagation of two particles (electrons or holes), each originating\nfrom a different probe electrode. The relevant processes are electron\ncotunneling through the superconductor and conversion of two electrons stemming\nfrom different probes in a Cooper pair. These processes are non-local and decay\nwhen the distance between the pair of involved contacts is larger than the\nsuperconducting coherence length. The conductance matrix of a the three\nterminal hybrid structure is calculated. The multi-probe processes enhance the\nconductance of each contact. If the contacts are magnetically polarized the\ncontribution of the various conduction channels may be separately detected.\n