Reveal the nematic topological superconductivity from the anisotropic unconventional Josephson effect: Theory and application to doped Bi2Se3

Abstract

We propose a scheme to reveal the possible nematic superconducting order parameter in the doped Bi 2 Se 3 by observing the anisotropic unconventional Josephson effect without an external magnetic field. We find the presence of an intrinsic π-phase in the spin-triplet channel of Andreev reflection. Its competition with the odd-parity superconducting gap phase can lead to unconventional Josephson effect in the Josephson junction, whose normal region is connected to the same side of the superconductor, called the U-shaped junction according to its geometry. For Josephson junctions with the interfaces perpendicular to the nematic direction, the competition will lead to a Josephson π-junctions. In the case where the interface is parallel to the nematic direction, it will lead to a Josephson 0-junction. Thus, this can directly reflect the nematic superconductivity. It is worth noting that Josephson coupling with the 4π period appears only in the normal injected channels. Interestingly, if the Josephson junction adopts a conventional geometry, it always exhibits a normal Josephson 0-junction regardless of the gap function taken by the doped Bi 2 Se 3 and therefore cannot distinguish the pairing symmetry. We thus propose a superconducting quantum interference device containing a U-shaped Josephson junction to detect nematic superconductivity. This proposal not only can be applied to detect nematic superconductivity but also provides a feasible platform for topological quantum computation.