Theory of superconductivity in SrPtAs

TL;DR

This paper develops models for SrPtAs, revealing that ferromagnetic fluctuations near a van Hove singularity induce f-wave triplet superconductivity, with SOC pinning the pairing orientation.

Contribution

It provides a detailed theoretical analysis of the pairing mechanism in SrPtAs, highlighting the role of specific orbitals, electron correlations, and spin-orbit coupling.

Findings

Active $(xz,yz)$-orbitals drive superconductivity.

Ferromagnetic fluctuations promote f-wave triplet pairing.

Superconducting T_c increases near van Hove singularity.

Abstract

We constructed tight-binding models for the new superconductor SrPtAs according to first principle calculations, and by functional renormalization group we investigated the effect of electron correlations and spin-orbital coupling (SOC) in Cooper pairing. We found that out of the five $d$-orbitals, the $(xz,yz)$-orbitals are the active ones responsible for superconductivity, and ferromagnetic fluctuations enhanced by the proximity to the van Hove singularity triggers $f$-wave triplet pairing. The superconducting transition temperature increases as the Fermi level is closer to the van Hove singularity until ferromagnetism sets in. The $d$-vector of the triplet pairing component is pinned by SOC along the out-of-plane direction. Experimental perspectives are discussed.