Metal-to-superconductor transition induced by lithium adsorption on monolayer 1T−Nb2C

Recently, two-dimensional ${\mathrm{Nb}}_{2}\mathrm{C}$ has garnered increasing attention, both experimentally and theoretically, due to its functional-group-dependent superconductivity. In contrast to the halogen and chalcogen additives that were the main focus of previous studies, we study the effect of lithium adsorption, which can also be incorporated during the synthesis of ${\mathrm{Nb}}_{2}\mathrm{C}$. Our computational analysis reveals a metal-to-superconductor transition in monolayer ${\mathrm{Nb}}_{2}\mathrm{C}$ with a critical temperature ${T}_{\mathrm{c}}$ of 22.1 K and a strong anisotropic superconducting gap distribution following the adsorption of lithium atoms. This emergent superconductivity is attributed to the increased number of electronic states at the Fermi energy, resulting from the contribution of Nb $d$ orbitals and electron gas states induced by the low electronegativity of lithium. Furthermore, the application of tensile strain raises the ${T}_{\mathrm{c}}$ to 24 K, which is higher than that of most functional-group-modified ${\mathrm{Nb}}_{2}\mathrm{C}$ systems. Our work deepens the understanding of electron-phonon coupling in layered ${\mathrm{Nb}}_{2}\mathrm{C}$ and provides insights into achieving high critical temperature superconductivity with a strong anisotropic superconducting gap distribution in this system.