Broken time-reversal symmetry in a new non-centrosymmetric superconductor Re8NbTa

Abstract

Re-based superconductors provide a rich platform for the study of unconventional superconductivity. We have investigated the superconducting properties of Re${}_8$NbTa, a new noncentrosymmetric cubic ($\hat{I}\pm$-Mn structure) rhenium-based ternary superconductor using transport, magnetization, specific heat, and muon spin rotation/relaxation ($\hat{I}¼$SR) measurements. Specific heat and transverse field $\hat{I}¼$SR measurements suggest moderately coupled fully gapped superconductivity, well described by BCS theory. However, our zero-field $\hat{I}¼$SR measurements reveal a small internal field onsetting around the superconducting T${}_c$, indicating that the superconducting order parameter breaks the time-reversal symmetry.

9 pages, 7 figures