Inter-orbital topological superconductivity in spin-orbit coupled superconductors with inversion symmetry breaking

TL;DR

This paper explores how spin-orbit coupling and inversion symmetry breaking in multi-orbital superconductors can stabilize topologically nontrivial spin-triplet states with point nodes, leading to unique spectral features.

Contribution

It demonstrates the possibility of topological superconductivity with spin-triplet pairing in systems lacking inversion symmetry, driven by orbital effects and spin-orbit coupling.

Findings

Topological spin-triplet superconducting states are stabilized without inversion symmetry.

Point nodes in the superconducting gap are protected by a non-zero winding number.

Lifshitz-type transitions can occur by tuning spin-orbit and inversion asymmetry parameters.

Abstract

We study the superconducting state of multi-orbital spin-orbit coupled systems in the presence of an orbitally driven inversion asymmetry assuming that the inter-orbital attraction is the dominant pairing channel. Although the inversion symmetry is absent, we show that superconducting states that avoid mixing of spin-triplet and spin-singlet configurations are allowed, and remarkably, spin-triplet states that are topologically nontrivial can be stabilized in a large portion of the phase diagram. The orbital-dependent spin-triplet pairing generally leads to topological superconductivity with point nodes that are protected by a nonvanishing winding number. We demonstrate that the disclosed topological phase can exhibit Lifshitz-type transitions upon different driving mechanisms and interactions, e.g., by tuning the strength of the atomic spin-orbit and inversion asymmetry couplings or by varying the doping and the amplitude of order parameter. Such distinctive signatures of the nodal phase manifest through an extraordinary reconstruction of the low-energy excitation spectra both in the bulk and at the edge of the superconductor.