Two-dimensional superconductors exfoliated from layered materials harbor novel superconductivity and exotic correlated phases, often concomitantly, but their discovery has been few and far between. Employing the anisotropic Migdal-Eliashberg formalism based on ab initio calculations, we find monolayer ${\mathrm{NiTe}}_2$ to be an intrinsic superconductor with a $T_{\text{c}}\sim 5.7$ K, although the bulk crystal is not known to superconduct. Remarkably, bilayer ${\mathrm{NiTe}}_2$ intercalated with lithium is found to display two-gap superconductivity with a critical temperature $T_{\text{c}}\sim 11.3$ K and a superconducting gap of $\sim 3.1$ meV, arising from a synergy of electronic and phononic effects. As monolayer and bilayer ${\mathrm{NiTe}}_2$ have been recently isolated experimentally, and lithium can be inserted into the bilayer via ionic liquid gating, the comparatively high $T_{\text{c}}$, substrate independence, and proximity tunability will make these superconductors ideal platforms for exploring intriguing correlation effects and quantum criticality associated two-dimensional superconductivity.

• Received 13 November 2019
• Revised 24 February 2020
• Accepted 26 February 2020

DOI:https://doi.org/10.1103/PhysRevB.101.100505