Mixed functionalization as a pathway to induce superconductivity in MXenes: vanadium and niobium carbide

The functionalization versatility of MXenes distinguishes them from other two-dimensional materials, enabling the design of numerous new materials with unique properties. By leveraging surface chemistry, functionalization allows for the manipulation of critical parameters such as the density of states and electron-phonon coupling, providing an excellent platform for exploring two-dimensional superconductivity. In this study, we investigate the impact of functionalization on vanadium carbide (V₂C) MXene, which is intrinsically non-superconducting, by considering three different cases: (i) hydrogen adatoms, (ii) fluorine adatoms, and (iii) mixed functionalization with hydrogen and fluorine adatoms. We confirm the mechanical and dynamical stability of functionalized V₂C using Born's stability criteria and phonon dispersion analyses. In all three cases, superconductivity emerges due to the presence of functional groups, which influence the electron-phonon interaction and electronic structure, leading to an enhanced electron-phonon coupling constant. The highest superconducting transition temperature is observed for mixed-functionalized V₂C, attributed to the softening of the ZA phonon mode along with high-energy phonon modes induced by hydrogen. To further explore the potential of mixed functionalization in inducing superconductivity, we extend our approach to another non-superconducting MXene, Nb₂C. The mixed-functionalized Nb₂C exhibits a superconducting transition temperature of 9.2 K, which surpasses the reported values for Nb₂CH₂, Nb₂CS₂, and Nb₂CBr₂. These findings underscore the effectiveness of mixed functionalization in enabling superconductivity in MXenes, paving the way for future theoretical and experimental investigations.