Superconductivity of monolayer Mo₂C: The key role of functional groups

Two-dimensional (2D) graphene-like MXenes have attracted enormous interest for their novel chemical and physical properties. Recently, 2D layered Mo₂C as a new member of Mxenes was formed from Mo₂Ga₂C thin films, which was found to be a promising candidate as a high-performance thermoelectric material. As the allotrope of 2D layered Mo₂C, the superconductivity was discovered in bulk α-Mo₂C. However, its superconducting transition temperature (T_C) was depressed from 4 K (thick film) to near 0 K when its thickness is less than 3.5 nm. In this report, according to the electron-phonon interaction, it is predicted that monolayer Mo₂C could be a quasi-two-dimensional superconductor and the effects of functional-groups are crucially important considering its unsaturated surface. Despite the suppressed superconductivity by chalcogen adsorption, our most interesting prediction is that the electron-phonon interaction of monolayer Mo₂C can be greatly enhanced by bromine absorption, suggesting that Mo₂CBr₂ as a good candidate for a nanoscale superconductor.