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

Abstract

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 [Baidya et al., Phys. Rev. B 104, 174510 (2021)] 2D van der Waals heterostructure comprising a single layer of MoS2 and few layers of NbSe2. We find strong EPC and a softening of phonon modes in the lowest acoustic branch. While the single MoS2 layer does not actively contribute to the EPC, it significantly elevates the superconducting critical temperature (Tc) compared to monolayer NbSe2. This is attributed to the degradation of the charge-density wave by the MoS2 layer. Notably, we observe a two-gap superconductivity in NbSe2/MoS2 and extend our study to three layers of NbSe2. A reduction in Tc with increasing thickness of NbSe2 is observed. Incorporation of spin-orbit coupling (SOC) suggests a possible mechanism for Ising superconductivity. We find that SOC reduces EPC while Tc is suppressed concomitantly by about 5K, leading to a closer estimate of the experimental Tc.

Source-reported materials — not catalogue approval

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