Microscopic investigation of the weakly correlated noncentrosymmetric superconductor SrAuSi$_3$

TL;DR

This study uses local probe techniques to reveal that SrAuSi3 is a weakly correlated, conventional BCS superconductor with weak electron correlations, providing insights into its electronic properties and pairing mechanism.

Contribution

It provides the first local-level investigation of SrAuSi3, demonstrating its weak correlations and conventional superconductivity, which aids in understanding the role of correlations in noncentrosymmetric superconductors.

Findings

Normal phase shows standard metallic behavior with weak correlations.

Superconducting phase exhibits BCS-type s-wave superconductivity.

Weak correlations allow for accurate band-structure calculations in SrAuSi3.

Abstract

SrAuSi$_3$ is a noncentrosymmetric superconductor (NCS) with $T_c$ = 1.54 K, which to date has been studied only via macroscopic techniques. By combining nuclear magnetic resonance (NMR) and muon-spin rotation ($\mu$SR) measurements we investigate both the normal and the superconducting phase of SrAuSi$_3$ at a local level. In the normal phase, our data indicate a standard metallic behavior with weak electron correlations and a Korringa constant $S_\mathrm{exp} = 1.31 \times 10^{-5}$ sK. The latter, twice the theoretical value, can be justified by the Moriya theory of exchange enhancement. In the superconducting phase, the material exhibits conventional BCS-type superconductivity with a weak-coupling s-wave pairing, a gap value $\Delta(0)$ = 0.213(2) meV, and a magnetic penetration depth $\lambda(0)$ = 398(2) nm. The experimental proof of weak correlations in SrAuSi$_{3}$ implies that correlation effects can be decoupled from those of antisymmetric spin-orbit coupling (ASOC), thus enabling accurate band-structure calculations in the weakly-correlated NCSs.