Multiple nodeless superconducting gaps in noncentrosymmetric superconductor PbTaSe2 with topological bulk nodal lines

TL;DR

This study reveals that PbTaSe2, a noncentrosymmetric superconductor with topological features, exhibits multiple nodeless superconducting gaps, indicating a fully gapped state that is compatible with topological superconductivity.

Contribution

The paper provides experimental evidence of multiple nodeless gaps in PbTaSe2, challenging the expectation of spin-triplet nodal states in noncentrosymmetric superconductors with strong spin-orbit coupling.

Findings

Negligible residual linear thermal conductivity in zero field

Field dependence of thermal conductivity shows an 'S'-shape curve

Supports the presence of multiple nodeless superconducting gaps

Abstract

Low-temperature thermal conductivity measurements were performed on single crystal of PbTaSe$_2$, a noncentrosymmetric superconductor with topological bulk nodal lines in the electronic band structure. It is found that the residual linear term $\kappa_0/T$ is negligible in zero magnetic field. Furthermore, the field dependence of $\kappa_0/T$ exhibits a clear "$S$"-shape curve. These results suggest that PbTaSe$_2$ has multiple nodeless superconducting gaps. Therefore, the spin-triplet state with gap nodes does not play an important role in this noncentrosymmetric superconductor with strong spin-orbital coupling. The fully gapped superconducting state also meets the requirement of a topological superconductor, if PbTaSe$_2$ is indeed the case.