We consider tunneling in a hybrid system consisting of a superconductor with
two or more probe electrodes which can be either normal metals or polarized
ferromagnets. In particular we study transport at subgap voltages and
temperatures. 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 originating
from a different probe electrode. The relevant processes are electron
cotunneling through the superconductor and conversion of two electrons stemming
from different probes in a Cooper pair. These processes are non-local and decay
when the distance between the pair of involved contacts is larger than the
superconducting coherence length. The conductance matrix of a the three
terminal hybrid structure is calculated. The multi-probe processes enhance the
conductance of each contact. If the contacts are magnetically polarized the
contribution of the various conduction channels may be separately detected.Comment: 7 pages, 1 figure, accepted in Europhysics Letters, minor changes, 3
references adde
