Enhancing superconductivity in MXenes through hydrogenation

TL;DR

This study shows that hydrogenation can significantly enhance superconductivity in MXenes, increasing critical temperatures and inducing superconductivity in previously non-superconducting materials through surface functionalization.

Contribution

The paper introduces a novel approach of using hydrogen adatoms to enhance and induce superconductivity in MXenes, supported by first-principles calculations and Eliashberg theory.

Findings

Hydrogenated Mo2N and W2N exhibit critical temperatures over 30 K.

Hydrogen adatoms modify phonon spectra and increase electron-phonon coupling.

Hydrogenation induces superconductivity in Nb2C, previously non-superconducting.

Abstract

Two-dimensional transition metal carbides and nitrides (MXenes) are an emerging class of atomically-thin superconductors, whose characteristics are highly prone to tailoring by surface functionalization. Here we explore the use of hydrogen adatoms to enhance phonon-mediated superconductivity in MXenes, based on first-principles calculations combined with Eliashberg theory. We first demonstrate the stability of three different structural models of hydrogenated Mo- and W-based MXenes. Particularly high critical temperatures of over 30 K are obtained for hydrogenated Mo$_2$N and W$_2$N. Several mechanisms responsible for the enhanced electron-phonon coupling are uncovered, namely (i) hydrogen-induced changes in the phonon spectrum of the host MXene, (ii) emerging hydrogen-based phonon modes, and (iii) charge transfer from hydrogen to the MXene layer, boosting the density of states at the Fermi level. Finally, we demonstrate that hydrogen adatoms are moreover able to induce superconductivity in MXenes that are not superconducting in pristine form, such as Nb$_2$C.