Creation of Spin-Triplet Cooper Pairs in the Absence of Magnetic Ordering

Daniel Breunig; Pablo Burset; Björn Trauzettel

doi:10.1103/PhysRevLett.120.037701

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Creation of Spin-Triplet Cooper Pairs in the Absence of Magnetic Ordering

Daniel Breunig, Pablo Burset, Björn Trauzettel

DOI 10.1103/PhysRevLett.120.037701 · Physical Review Letters

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Abstract

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.