Anisotropic multiband superconductivity in 2M-WS2 probed by controlled disorder

The intrinsically superconducting Dirac semimetal 2M-WS2 is a promising candidate for realizing proximity-induced topological superconductivity in its protected surface states. A precise characterization of the bulk superconducting state is essential to understand the nature of surface superconductivity in the system. Here, we report a detailed experimental study of the temperature-dependent London penetration depth, λ(T), the upper critical field, Hc2(T), and the effects of nonmagnetic disorder on these quantities, as well as on the superconducting transition temperature Tc in single crystals of 2M-WS2. We observe a power-law variation of λ(T)∝ T3 at temperatures below 0.35Tc. Nonmagnetic pointlike disorder induced by 2.5 MeV electron irradiation at various doses results in a significant suppression of Tc. These observations are markedly different from expectations for a fully gapped isotropic s-wave superconductor. Together with the substantial increase of slope, dHc2/dT|T=Tc, with increasing disorder, our results suggest a strongly anisotropic s++ multiband superconducting state. These results have direct consequences for the expected proximity-induced superconductivity of the topological surface states.