Fully gapped superconductivity and topological aspects of the noncentrosymmetric superconductor TaReSi

We report a study of the noncentrosymmetric TaReSi superconductor by means of the muon-spin rotation and relaxation (μSR) technique, complemented by electronic band-structure calculations. Its superconductivity, with Tc=5.5K and upper critical field μ0Hc2(0)∼3.4T, was characterized via electrical-resistivity and magnetic-susceptibility measurements. The temperature-dependent superfluid density, obtained from transverse-field μSR, suggests a fully gapped superconducting state in TaReSi, with an energy gap Δ0=0.79meV and a magnetic penetration depth λ0=562nm. The absence of a spontaneous magnetization below Tc, as confirmed by zero-field μSR, indicates a preserved time-reversal symmetry in the superconducting state. The density of states near the Fermi level is dominated by the Ta- and Re-5d orbitals, which account for the relatively large band splitting due to the antisymmetric spin-orbit coupling. In its normal state, TaReSi behaves as a three-dimensional Kramers nodal-line semimetal, characterized by an hourglass-shaped dispersion protected by glide reflection. By combining nontrivial electronic bands with intrinsic superconductivity, TaReSi is a promising material for investigating the topological aspects of noncentrosymmetric superconductors.