Muon spin rotation and relaxation study on topological noncentrosymmetric superconductor PbTaSe$_2$

TL;DR

This study uses muon spin rotation and relaxation experiments to investigate the superconducting gap symmetry and time-reversal symmetry in the topological noncentrosymmetric superconductor PbTaSe$_2$, revealing a fully-gapped isotropic superconducting state.

Contribution

It provides the first detailed muon spin rotation/relaxation analysis of PbTaSe$_2$, demonstrating a fully-gapped superconducting state and no internal magnetic fields, advancing understanding of its topological superconductivity.

Findings

No internal magnetic field in the superconducting state.

Superconducting gap is isotropic and fully gapped.

Supports the classification of PbTaSe$_2$ as a topological superconductor.

Abstract

Topological superconductivity is an exotic phenomenon due to the symmetry-protected topological surface state, in which a quantum system has an energy gap in the bulk but supports gapless excitations confined to its boundary. Symmetries including central and time-reversal (TRS), along with their relations with topology, are crucial for topological superconductivity. We report muon spin relaxation/rotation ($\mu$SR) experiments on a topological noncentrosymmetric superconductor PbTaSe$_2$ to study its TRS and gap symmetry. Zero-field $\mu$SR experiments indicate the absence of internal magnetic field in the superconducting state, consistent with previous $\mu$SR results. Furthermore, transverse-field $\mu$SR measurements reveals that the superconducting gap of PbTaSe$_2$ is an isotropic three-dimensional fully-gapped single-band. The fully-gapped results can help understand the pairing mechanism and further classify the topological superconductivity in this system.