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

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 ($\hat{I}¼$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 $S_{\exp }=1.31\times 10^{-5}$ 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 $\hat{I}”(0)$ = 0.213(2) meV, and a magnetic penetration depth $\hat{I}»(0)$ = 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.

6 pages, 9 figures