Nodeless superconducting gap in the topological superconductor candidate 2M–WS2

Abstract

Recently, a new transition-metal dichalcogenide (TMD) material $2M$-phase ${\mathrm{WS}}_{2}$ was synthesized. The material $2M\text{\ensuremath{-}}{\mathrm{WS}}_{2}$ not only exhibits superconductivity, with the highest ${T}_{\text{c}}$ being 8.8 K at ambient pressure among TMDs, but also hosts a topological surface state. Here we report the low-temperature thermal conductivity measurements on $2M\text{\ensuremath{-}}{\mathrm{WS}}_{2}$ single crystals to investigate its superconducting gap structure. A negligible residual linear term ${\ensuremath{\kappa}}_{0}/T$ in zero field shows that $2M\text{\ensuremath{-}}{\mathrm{WS}}_{2}$ has a fully superconducting gap with all electrons paired. The field dependence of ${\ensuremath{\kappa}}_{0}/T$ suggests an anisotropic superconducting gap or multiple nodeless superconducting gaps in $2M\text{\ensuremath{-}}{\mathrm{WS}}_{2}$. Such a fully gapped superconducting state is compatible with $2M\text{\ensuremath{-}}{\mathrm{WS}}_{2}$ being a topological superconductor candidate.