Probing the superconducting gap structure in the noncentrosymmetric topological superconductor ZrRuAs

TL;DR

This study investigates the superconducting gap structure of ZrRuAs, a noncentrosymmetric topological superconductor candidate, using muon spin rotation and other measurements, revealing an isotropic s-wave gap and preserved time-reversal symmetry.

Contribution

First comprehensive muon spin rotation study confirming isotropic s-wave gap and time-reversal symmetry in ZrRuAs, a noncentrosymmetric topological superconductor candidate.

Findings

Bulk superconductivity below 7.9 K confirmed by multiple measurements

Superconducting gap is isotropic s-wave as per TF-$b$SR and heat capacity analysis

Time-reversal symmetry remains intact in the superconducting state

Abstract

The superconducting gap structure of a topological crystalline insulator (TCI) candidate ZrRuAs ($T^{\rm on}_{\rm c}$ = 7.9(1) K) with a noncentrosymmetric crystal structure has been investigated using muon spin rotation/relaxation ($\mu$SR) measurements in transverse-field (TF) and zero-field (ZF) geometries. We also present the results of magnetization, electrical resistivity and heat capacity measurements on ZrRuAs, which reveal bulk superconductivity below 7.9~K. The temperature dependence of the effective penetration depth obtained from the analysis of the TF-$\mu$SR spectra below $T_{\rm c}$ is well described by an isotropic $s$-wave gap model as also inferred from an analysis of the heat capacity in the superconducting state. ZF $\mu$SR data do not show any significant change in the muon spin relaxation rate above and below the superconducting transition temperature indicating that time-reversal symmetry is preserved in the superconducting state of this material.