Nodeless superconductivity in the noncentrosymmetric ThIrSi compound

TL;DR

This study reveals that ThIrSi is a nodeless superconductor with multiple gaps and preserved time-reversal symmetry, characterized by local-probe techniques indicating unconventional superconducting features due to its noncentrosymmetric structure.

Contribution

It provides the first comprehensive local-probe investigation of ThIrSi, demonstrating nodeless, multi-gap superconductivity with preserved time-reversal symmetry.

Findings

Nodeless superconductivity confirmed by { extmu}SR and NMR.

Presence of multiple superconducting gaps.

No spontaneous magnetic fields below T_c, indicating preserved time-reversal symmetry.

Abstract

The ThIrSi superconductor, with $T_c = 6.5$ K, is expected to show unusual features in view of its noncentrosymmetric structure and the presence of heavy elements featuring a sizable spin-orbit coupling. Here, we report a comprehensive study of its electronic properties by means of local-probe techniques: muon-spin rotation and relaxation ({\textmu}SR) and nuclear magnetic resonance (NMR). Both the superfluid density $\rho_\mathrm{sc}(T)$ (determined via transverse-field {\textmu}SR) and the spin-lattice relaxation rate $T_1^{-1}(T)$ (determined via NMR) suggest a nodeless superconductivity. Furthermore, the absence of spontaneous magnetic fields below $T_c$, as evinced from zero-field {\textmu}SR measurements, indicates a preserved time-reversal symmetry in the superconducting state of ThIrSi. Temperature-dependent upper critical fields as well as field-dependent superconducting muon-spin relaxations suggest the presence of multiple superconducting gaps in ThIrSi.