Probing the superconducting gap structure in the noncentrosymmetric topological superconductor ZrRuAs

The superconducting gap structure of the topological superconductor candidate ZrRuAs with a noncen- trosymmetric crystal structure has been investigated using muon-spin rotation/relaxation (μSR) measurements in transverse-field (TF) and zero-field (ZF) geometries. Magnetization, electrical resistivity, and heat capacity measurements reveal bulk superconductivity below a superconducting transition temperature T_c = 7.9(1) K. The temperature dependence of the effective penetration depth obtained from the TF-μSR spectra, and the electronic heat capacity in the superconducting state, are well described by an isotropic s-wave gap model. Comparison of the electronic mean free path with the superconducting coherence length suggests superconductivity in the dirty limit. ZF μSR data show there is no significant change in the muon-spin relaxation rate above and below T_c, indicating that time-reversal symmetry is preserved in the superconducting state.