Microscopic investigation of the weakly correlated noncentrosymmetric superconductor 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 (µSR) 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 × 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 ∆(0) = 0.213(2) meV, and a magnetic penetration depth λ(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.