Spectroscopic evidence of multi-gap superconductivity in non-centrosymmetric AuBe

Abstract

AuBe is a chiral, non-centrosymmetric superconductor with transition temperature $T_C$ $\simeq$ 3.25 K. The broken inversion symmetry in its crystal structure makes AuBe a possible candidate to host a mixed singlet-triplet pairing symmetry in its superconducting order parameter ($\Delta$). This possibility was investigated by transport, thermodynamic, and muon-spin rotation/relaxation experiments in AuBe. However, this issue was not addressed using direct spectroscopic probes so far. In addition, certain ambiguities exist in the description of superconductivity in AuBe based on $\mu$SR experiments reported earlier. Here we report scanning tunneling spectroscopy (STS) on AuBe down to 300 mK. We found a signature of two superconducting gaps (with 2${\Delta }_1/k_B{T}_C$ = 4.37 and 2${\Delta }_2/k_B{T}_C$ = 2.46 respectively) and a clean BCS-like temperature dependence of both the gaps. We have also performed band structure calculations to identify the different bands that might give rise to the observed two-gap superconductivity in AuBe.

Added fresh analysis based on additional data. Added band structure calculations. Corrected typos. Added references. Updated author list. To appear in $\text{Physical Review B}$

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