Spin Currents and Spontaneous Magnetization at Twin Boundaries of Noncentrosymmetric Superconductors

TL;DR

This paper theoretically investigates twin boundaries in noncentrosymmetric superconductors, revealing how parity mixing induces spin currents, spontaneous local time-reversal symmetry breaking, and phase transitions leading to spin magnetization and supercurrents.

Contribution

It provides a self-consistent analysis of twin boundary phenomena in noncentrosymmetric superconductors, highlighting new phases with spin currents and local symmetry breaking.

Findings

Twin boundaries support spin currents due to parity mixing.

Spontaneous local time-reversal symmetry breaking occurs near twin boundaries.

Secondary phase transition induces spin magnetization and orbital supercurrents.

Abstract

Twin boundaries are generic crystalline defects in noncentrosymmetric crystal structures. We study theoretically twin boundaries in time-reversal symmetric noncentrosymmetric superconductors that admit parity-mixed Cooper pairing. Twin boundaries support spin currents as a consequence of this parity mixing. If the singlet and triplet components of the superconducting order parameter are of comparable magnitude, the superconducting state breaks spontaneously the bulk time-reversal symmetry locally near the twin boundary. By self-consistently evaluating the Bogoliubov-de-Gennes equations and the gap functions we find two distinct phases: First, time-reversal symmetry breaking enhances the spin currents but does not lead to chiral supercurrents. A secondary phase transition then triggers a spin magnetization and an orbital supercurrent near the twin boundary.