Superconducting and normal state properties of noncentrosymmetric superconductor NbOs${}_2$ investigated by muon spin relaxation and rotation

Abstract

Noncentrosymmetric superconductors with $\alpha$-manganese structure has attracted much attention recently, after the discovery of time-reversal symmetry breaking in all the members of Re${}_6$X (X = Ti, Hf, Zr) family. Similar to Re${}_6$X, NbOs${}_2$ also adopts $\alpha$-$Mn$ structure and found to be superconducting with critical temperature $T_c$ $\approx$ 2.7 K. The results of the resistivity, magnetization, specific heat and muon-spin relaxation/rotation measurements show that NbOs${}_2$ is a weakly coupled type-II superconductor. Interestingly, the zero-field muon experiments indicate that the time-reversal symmetry is preserved in the superconducting state. The low-temperature transverse-field muon measurements and the specific heat data evidence a conventional isotropic fully gapped superconductivity. However, the calculated electronic properties in this material show that the NbOs${}_2$ is positioned close to the band of unconventionality of the Uemura plot, indicating that NbOs${}_2$ potentially borders an unconventional superconducting ground state.

12 pages, 7 figures Accepted Physical Review B