Electron-phonon coupling, critical temperatures, and gaps in NbSe2/MoS2 Ising superconductors

Utilizing Migdal-Eliashberg theory of superconductivity within the first-principles calculations, we work out the role of electron-phonon coupling (EPC) and anisotropic superconducting properties of a recently discovered [PRB 104, 174510 (2021)] 2D van der Waals heterostructure comprising a single layer of MoS 2 and few layers of NbSe 2 .We find strong EPC and a softening of phonon modes in the lowest acoustic branch.While the single MoS 2 layer does not actively contribute to the EPC, it significantly elevates the superconducting critical temperature (T c ) compared to monolayer NbSe 2 .This is attributed to the degradation of the charge-density wave (CDW) by the MoS 2 layer.Notably, we observe a two-gap superconductivity in NbSe 2 /MoS 2 and extend our study to three layers of NbSe 2 .A reduction in T c with increasing thickness of NbSe 2 is observed.We confirm that this trend is consistent with recent experiments, if one goes beyond three layers of NbSe 2 .Incorporation of spin-orbit coupling (SOC) suggests a possible mechanism for Ising superconductivity.We find that SOC reduces EPC while T c is suppressed concomitantly by about 5K, leading to a closer estimate of the experimental T c .