Intrinsic Andreev $\pi$-reflection and Josephson $\pi$-junction for centrosymmetric spin-triplet superconductors

TL;DR

This paper explores how intrinsic Andreev π-phase and orbital-phase influence Josephson effects in centrosymmetric spin-triplet superconductors, proposing a method to identify pairing symmetry via a U-shaped Josephson junction.

Contribution

It introduces the concepts of Andreev π-phase and orbital-phase in odd-parity pairings and analyzes their impact on Josephson junction behavior in centrosymmetric spin-triplet superconductors.

Findings

Intrinsic π-phase exists between spin-triplet Cooper pairs in Andreev reflections.

Competition between phases can produce a Josephson π-junction with unique geometry.

The interplay of phases affects the CPR, leading to 0-junctions regardless of pairing symmetry.

Abstract

In this work, we systematically study two phases, called Andreev $\pi$-phase and orbital-phase, and their influence on the Josephson effect. When the system is time-reversal invariant and centrosymmetric, these two phases only appear in the odd-parity pairings. The Andreev $\pi$-phase has nothing to do with the specific form of the odd-parity pairings and means an intrinsic $\pi$-phase between the spin-triplet Cooper pairs entering and leaving CTSCs in the Andreev reflections. The orbital-phase corresponds to the phase difference between the spin-triplet Cooper pairs with opposite spin polarization and depends on the specific form of the odd-parity gap functions. When the normal region of the Josephson junction contacts the same side of the CTSCs with some specific odd-parity parings, the competition between the two phases can lead to the Josephson $\pi$-junction. Note that this junction is different from that of the conventional Josephson junction (JJ) and is dubbed a U-shaped junction according to its geometry. Meanwhile, in a conventional JJ, the interplay of these two phases causes their impact on the CPR to be completely canceled out. Therefore no matter what kind of pairing symmetries the CTSC has, it will lead to Josephson 0-junction in this case. We obtain our results based on the model of the M$_{x}$Bi$_2$Se$_3$ family where M may be Cu, Sr, or Nb. Therefore, we propose to detect the pairing symmetry of M$_{x}$Bi$_2$Se$_3$ through a superconducting quantum interference device containing a U-shaped Josephson junction.