Two-dimensional (2D) superconductors have attracted great attention in recent years due to the possibility of new phenomena in lower dimensions. With many bulk transition metal carbides being well-known conventional superconductors, here we perform first-principles calculations to evaluate the possible superconductivity in a 2D monolayer Mo2C. Three candidate structures (monolayer alpha-Mo2C, 1T MXene-Mo2C, and 2H MXene-Mo2C) are considered and the most stable form is found to be the 2H MXene-Mo2C. Electronic structure calculations indicate that both unpassivated and passivated 2H forms exhibit metallic properties. We obtain the phonon frequencies and electron-phonon couplings using density-functional perturbation theory, and based on the BCS theory and McMillan equation, estimate the critical temperatures to be in the ~0-13 K range, depending on the species of the surface termination (O, H and OH). The most interesting termination group is H, which can increase the electron-phonon coupling and bring the critical temperature to 13 K. This shows a rather high critical temperature, tunable by surface termination, making this 2D carbide an interesting test bed for low-dimensional superconductivity.
@article{arxiv.1702.03373,
title = {Predicting Stable Phase Monolayer Mo$_2$C (MXene), a Superconductor with Chemically-Tunable Critical Temperature},
author = {Jincheng Lei and Alex Kutana and Boris I. Yakobson},
journal= {arXiv preprint arXiv:1702.03373},
year = {2017}
}