  Nonlocal charge correlations induced in two normal metals contacted
separately to a supercon- ductor have been studied intensively in the past few
years. Here we investigate nonlocal correlations induced by the transfer of
pure spin currents through a superconductor on a scale comparable to the
superconducting coherence length. As with charge currents, two processes
contribute to the nonlocal spin signal: crossed Andreev reflection (CAR), where
an electron with spin up injected from one normal metal into the superconductor
results in a hole with spin down being injected into the second normal metal,
and elastic cotunneling (EC), where the electron with spin up injected from the
first normal metal results in an electron with spin up being injected into the
second normal metal. Unlike charge currents, however, the spin currents
associated with CAR and EC add due to the fact that the bulk superconductor
cannot sustain a net spin current.
