A note on the upper critical field of Sr$_2$RuO$_4$ under strain

TL;DR

This paper analyzes how strain affects the upper critical field in Sr$_2$RuO$_4$, incorporating a new inter-orbital suppression mechanism alongside traditional effects, suggesting triplet pairing and proposing further experiments.

Contribution

It extends the analysis of the upper critical field in Sr$_2$RuO$_4$ under strain by including a novel inter-orbital effect, challenging the singlet pairing assumption.

Findings

Standard orbital effect and inter-orbital mechanism explain critical field changes.

Strain enhances critical field while reducing anisotropy.

Triplet pairing remains a viable explanation for observations.

Abstract

In the light of the recently discussed mechanism for suppression of superconductivity in multi-orbital systems called inter-orbital effect, here we extend our analysis of the upper critical field in Sr$_2$RuO$_4$ now under strain. We show that the presence of the standard orbital effect and the new mechanism can consistently account for the qualitative changes observed in the upper critical field for the strained system, in particular, combining the overall enhancement of the critical field with the reduction in the anisotropy. The proposed picture holds for a triplet superconducting state, showing that a singlet state is not the only possibility to account for the observations. We suggest further experiments in order to clarify our understanding about the superconducting phase of Sr$_2$RuO$_4$.