Spin response and topology of a staggered Rashba superconductor

TL;DR

This paper explores how local inversion symmetry breaking in layered superconductors with strong spin-orbit coupling affects spin response and topological phases, with implications for materials like CeRh2As2.

Contribution

It reveals persistent signatures of local non-centrosymmetry in spin susceptibility and identifies potential topological superconducting regimes in a layered system.

Findings

Increased spin susceptibility in spin-singlet superconductors at low temperatures.

Direction-dependent spin response distinguishes superconducting order parameters.

Multiple regimes with possible topological superconducting phases identified.

Abstract

Inversion symmetry is a key symmetry in unconventional superconductors and even its local breaking can have profound implications. For inversion-symmetric systems, there is a competition on a microscopic level between the spin-orbit coupling associated with the local lack of inversion and hybridizing terms that `restore' inversion. Investigating a layered system with alternating mirror-symmetry breaking, we study this competition considering the spin response of different superconducting order parameters for the case of strong spin-orbit coupling. We find that signatures of the local non-centrosymmetry, such as an increased spin susceptibility in spin-singlet superconductors for $T\rightarrow 0$, persist even into the quasi-three-dimensional regime. This leads to a direction dependent spin response which allows to distinguish different superconducting order parameters. Furthermore, we identify several regimes with possible topological superconducting phases within a symmetry-indicator analysis. Our results may have direct relevance for the recently reported Ce-based superconductor CeRh$_2$As$_2$ and beyond.