Anisotropic Full-Gap Superconductivity in 2M-WS Topological Metal with Intrinsic Proximity Effect.

Layered 2M-WS is recently observed to show Majorana bound states in vortices, but its superconducting pairing mechanism remains unknown, hindering the understanding of its topological superconducting nature. Using the Migdal-Eliashberg theory and electron-phonon Wannier interpolation, we demonstrate that both bulk and bilayer 2M-WS have a single anisotropic full-gap superconducting order of s-wave symmetry. We successfully reproduce the experimental superconducting critical temperature for the bulk and predict the bilayer 2M-WS, a two-dimensional (2D) topological metal with nontrivial edge states right at the Fermi energy, to superconduct at 7 K, much higher than that in most 2D transition metal dichalcogenides (TMDs). A distinct proximity-enhanced surface superconductivity is further revealed by simulating quasiparticle density of states. This work unveils a universal electron-phonon full-gap pairing in 2M group VI TMDs and suggests a strong intrinsic surface-bulk proximity effect for 2M-WS, paving the way to engineering topological superconductivity in TMD-based nanoscale devices.