Strong electron–phonon coupling and predicted high superconducting transition temperature of MXenes revealed in 2H-Mo2N under biaxial stress

Abstract

Extensive investigations have been conducted on Mo-based MXenes due to their high superconducting temperatures ($T_c$). This work theoretically reports strong electron–phonon coupling (EPC) and high $T_c$ ($\approx$38 K) of 2H-Mo${}_2$N under biaxial stress, with excellent mechanical properties. EPC and $T_c$ are elucidated upon dynamically stable strain range. At 0% strain, EPC constant ($\lambda$) and $T_c$ are 1.32 and 22.7 K, respectively. They are improved when subjected to biaxial stresses. Strong EPC with $\lambda$ over 2.0 occurs at −4%, −2.5%, and 5% strains, yielding enhanced $T_c$. The finding suggests that the energy levels of electronic bands at the Fermi level are enhanced by strain, which enhances EPC. Moreover, the impact of functional groups on superconductivity has been investigated. The $\lambda$’s of Mo${}_2$NH${}_2$ and Mo${}_2$NO${}_2$ are reduced, and $T_c$ drops nearly to 20.0 and 0.9 K, respectively. This work provides an example of designing 2D superconductors by tuning atomic recipes and strain-dependent engineering.