Locally Non-centrosymmetric Superconductivity in Multilayer Systems

TL;DR

This paper investigates how local inversion symmetry breaking in multilayer superconductors with inhomogeneous Rashba spin-orbit coupling affects their electronic properties, revealing unique superconducting behaviors and spin susceptibility enhancements.

Contribution

It introduces a detailed analysis of superconductivity in multilayer systems with local inversion symmetry breaking and inhomogeneous Rashba coupling, highlighting the role of phase differences between layers.

Findings

Rashba spin-orbit coupling enhances spin susceptibility.

Spin susceptibility depends on phase difference of order parameters.

Local inversion symmetry breaking leads to unique superconducting properties.

Abstract

Although multilayer systems possess global inversion symmetry, some of the layers lack local inversion symmetry because no global inversion centers are present on such layers. Such locally non-centrosymmetric systems exhibit spatially modulated Rashba spin-orbit coupling. In this study, the superconductivity in multilayer models exhibiting inhomogeneous Rashba spin-orbit coupling is investigated. We study the electronic structure, superconducting gap, and spin susceptibility in the superconducting state with mixed parity order parameters. We show the enhancement of the spin susceptibility by Rashba spin-orbit coupling and interpret it on the basis of the crossover from a centrosymmetric superconductor to a non-centrosymmetric superconductor. It is also shown that the spin susceptibility is determined by the phase difference of the order parameter between layers and is nearly independent of the parity mixing of order parameters. An intuitive understanding is given on the basis of the analytic expression of superconducting order parameters in the band basis. The results indicate that not only a broken global inversion symmetry but also a broken local inversion symmetry leads to unique properties of superconductivity. We discuss the superconductivity in artificial superlattices involving CeCoIn5 and multilayer high-Tc cuprates.