Enhanced and Tunable Superconductivity Enabled by Mechanically Stable Halogen-Functionalized Mo2C MXenes

TL;DR

This study uses first-principles calculations to show that halogen-functionalized Mo2C MXenes, especially with Br and I, are mechanically stable 2D superconductors with tunable high transition temperatures, significantly surpassing pristine Mo2C.

Contribution

It reveals that halogen functionalization enhances superconductivity in Mo2C MXenes and demonstrates tunability via doping and strain, providing new pathways for 2D superconductor design.

Findings

Br- and I-functionalized Mo2C are dynamically stable.

Superconducting Tc reaches up to 18.1 K for Mo2CI2.

Carrier doping can increase Tc up to ~21.7 K.

Abstract

We present a comprehensive first-principles investigation of the structural, electronic, vibrational, and superconducting properties of halogen-functionalized Mo2YX2 (Y = C, N; X = F, Cl, Br, I) MXene monolayers. Density functional theory and density functional perturbation theory calculations reveal that, among the halogenated systems considered, only Br- and I-functionalized Mo2C monolayers are dynamically stable, as confirmed by positive definite phonon spectra throughout the Brillouin zone. Electronic structure calculations show metallic behavior with states near the Fermi level dominated by Mo d orbitals with pronounced electronic density of states, providing favorable conditions for strong electron-phonon coupling (EPC). The resulting EPC constants place both systems in the strong coupling regime, yielding superconducting transition temperatures of Tc = 13.1 K for Mo2CBr2 and Tc = 18.1 K for Mo2CI2 within the Allen-Dynes formalism. Notably, halogen functionalization itself plays a crucial role in enhancing superconductivity in Mo2C, which has Tc = 7.2 K, leading to a substantial increase in the superconducting transition temperature compared with pristine Mo2C through strengthened electron-phonon coupling. Furthermore, we demonstrate that superconductivity in these systems is highly tunable via carrier doping and biaxial tensile strain. Electron doping significantly enhances EPC and raises Tc up to 21.7 K for Mo2CBr2 and 21.3 K for Mo2CI2. Our results identify halogen-functionalized Mo2C MXenes as mechanically robust, phonon mediated two dimensional superconductors and highlight carrier doping as an effective strategy for optimizing their superconducting performance.