Unusual $H$-$T$ phase diagram of CeRh$_2$As$_2$ -- the role of staggered non-centrosymmetricity

TL;DR

This paper investigates the complex superconducting phase diagram of CeRh$_2$As$_2$, revealing how alternating Rashba spin-orbit coupling influences the order parameter and leads to unusual magnetic responses and phase transitions.

Contribution

It introduces a generalized Ginzburg-Landau model for layered superconductors with staggered spin-orbit coupling, explaining the unusual $H$-$T$ phase diagram of CeRh$_2$As$_2$.

Findings

Identification of a kink in the upper critical field.

Observation of a first-order phase transition within the mixed phase.

Role of internal phase transition in the $H$-$T$ phase diagram.

Abstract

Superconductivity in a crystalline lattice without inversion is subject to complex spin-orbit-coupling effects, which can lead to mixed-parity pairing and an unusual magnetic response. In this study, the properties of a layered superconductor with alternating Rashba spin-orbit coupling in the stacking of layers, hence (globally) possessing a center of inversion, is analyzed in an applied magnetic field, using a generalized Ginzburg-Landau model. The superconducting order parameter consists of an even- and an odd-parity pairing component which exchange their roles as dominant pairing channel upon increasing the magnetic field. This leads to an unusual kink feature in the upper critical field and a first-order phase transition within the mixed phase. We investigate various signatures of this internal phase transition. The physics we discuss here could explain the recently found $H$--$T$ phase diagram of the heavy Fermion superconductor CeRh$_2$As$_2$.