In superconducting spintronics, it is essential to generate spin-triplet
Cooper pairs on demand. Up to now, proposals to do so concentrate on hybrid
structures in which a superconductor (SC) is combined with a magnetically
ordered material (or an external magnetic field). We, instead, identify a novel
way to create and isolate spin-triplet Cooper pairs in the absence of any
magnetic ordering. This achievement is only possible because we drive a system
with strong spin-orbit interaction--the Dirac surface states of a strong
topological insulator (TI)--out of equilibrium. In particular, we consider a
bipolar TI-SC-TI junction, where the electrochemical potentials in the outer
leads differ in their overall sign. As a result, we find that nonlocal singlet
pairing across the junction is completely suppressed for any excitation energy.
Hence, this junction acts as a perfect spin triplet filter across the SC
generating equal-spin Cooper pairs via crossed Andreev reflection.Comment: 12 pages, 8 figure
