Effects of paramagnetic pair-breaking and spin-orbital coupling on multi-band superconductivity

TL;DR

This paper investigates how paramagnetic pair-breaking and spin-orbital coupling influence multi-band superconductivity, revealing enhanced critical fields and proposing a model that aligns well with experimental data from Nd-doped SrTiO3 films.

Contribution

It introduces a model incorporating orbital, paramagnetic, and spin-orbital effects to analyze critical fields in multi-band superconductors, supported by experimental data.

Findings

Enhanced out-of-plane critical field exceeding the Pauli limit.

Good agreement between the proposed model and experimental data.

Multi-band effects significantly impact critical field behavior.

Abstract

The BCS picture of superconductivity describes pairing between electrons originating from a single band. A generalization of this picture occurs in multi-band superconductors, where electrons from two or more bands contribute to superconductivity. The contributions of the different bands can result in an overall enhancement of the critical field and can lead to qualitative changes in the temperature dependence of the upper critical field when compared to the single-band case. While the role of orbital pair-breaking on the critical field of multi-band superconductors has been explored extensively, paramagnetic and spin-orbital scattering effects have received comparatively little attention. Here we investigate this problem using thin films of Nd-doped SrTiO$_3$. We furthermore propose a model for analyzing the temperature-dependence of the critical field in the presence of orbital, paramagnetic and spin-orbital effects, and find a very good agreement with our data. Interestingly, we also observe a dramatic enhancement in the out-of-plane critical field to values well in excess of the Chandrasekhar-Clogston (Pauli) paramagnetic limit, which can be understood as a consequence of multi-band effects in the presence of spin-orbital scattering.