Fully gapped superconductivity and topological aspects of the noncentrosymmetric superconductor TaReSi

Abstract

We report a study of the noncentrosymmetric TaReSi superconductor by means of the muon-spin rotation and relaxation $(\ensuremath{\mu}\mathrm{SR})$ technique, complemented by electronic band-structure calculations. Its superconductivity, with ${T}_{c}=5.5\phantom{\rule{0.28em}{0ex}}\text{K}$ and upper critical field ${\ensuremath{\mu}}_{0}{H}_{\mathrm{c}2}(0)\ensuremath{\sim}3.4\phantom{\rule{0.28em}{0ex}}\text{T}$, was characterized via electrical-resistivity and magnetic-susceptibility measurements. The temperature-dependent superfluid density, obtained from transverse-field $\ensuremath{\mu}\mathrm{SR}$, suggests a fully gapped superconducting state in TaReSi, with an energy gap ${\mathrm{\ensuremath{\Delta}}}_{0}=0.79\phantom{\rule{0.28em}{0ex}}\text{meV}$ and a magnetic penetration depth ${\ensuremath{\lambda}}_{0}=562\phantom{\rule{0.28em}{0ex}}\text{nm}$. The absence of a spontaneous magnetization below ${T}_{c}$, as confirmed by zero-field $\ensuremath{\mu}\mathrm{SR}$, 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-$5d$ 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.