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 (μ SR ) technique, complemented by electronic band-structure calculations. Its superconductivity, with Tc=5.5 K and upper critical field μ0Hc 2(0 ) ∼3.4 T , was characterized via electrical-resistivity and magnetic-susceptibility measurements. The temperature-dependent superfluid density, obtained from transverse-field μ SR , suggests a fully gapped superconducting state in TaReSi, with an energy gap Δ0=0.79 meV and a magnetic penetration depth λ0=562 nm . The absence of a spontaneous magnetization below Tc, as confirmed by zero-field μ SR , 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-5 d 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.