Superconductivity in functionalized niobium-carbide MXenes

TL;DR

This study uses first-principles calculations to show that functionalizing niobium carbide MXenes with Cl and S can induce and enhance superconductivity, with potential transition temperatures up to 40 K, opening new pathways for MXene-based superconductors.

Contribution

The paper demonstrates that Cl and S functionalization can induce and significantly enhance superconductivity in niobium carbide MXenes, including predictions of high transition temperatures.

Findings

Bulk Nb₂CCl₂ has a Tc of 6 K, matching experiments.

Monolayer Nb₂CCl₂ shows increased Tc up to 10 K.

Gate doping can raise Tc up to 40 K.

Abstract

We show the effect of Cl and S functionalization on the superconducting properties of layered (bulk) and monolayer niobium carbide (Nb$_2$C) MXene crystals, based on first-principles calculations combined with Eliashberg theory. For the bulk layered Nb$_2$CCl$_2$, the calculated superconducting transition temperature ($T_c$) is in very good agreement with the recently measured value of 6 K. We show that $T_c$ is enhanced to 10 K for monolayer Nb$_2$CCl$_2$, due to an increase in the density of states at the Fermi level, and the corresponding electron-phonon coupling. We further demonstrate a feasible gate-induced enhancement of $T_c$ up to 40 K for both bulk-layered and monolayer Nb$_2$CCl$_2$ crystals. For the S-functionalized cases our calculations reveal the importance of phonon softening in understanding their superconducting properties. Finally, we predict that Nb$_3$C$_2$S$_2$ in bulk-layered and monolayer form is potentially superconducting, with a $T_c$ around 30 K. Considering that Nb$_2$C is not superconducting in pristine form, our findings promote functionalization as a pathway towards robust superconductivity in MXenes.