# Hydrogen-induced high-temperature superconductivity in two-dimensional materials: Example of hydrogenated monolayer MgB$_2$

## TL;DR

This paper demonstrates that hydrogen adatoms can significantly enhance superconductivity in two-dimensional materials, exemplified by monolayer MgB$_2$, achieving critical temperatures over 100 K under strain.

## Contribution

It introduces a novel approach of using hydrogenation to induce high-temperature superconductivity in 2D materials, supported by first-principles calculations and Eliashberg theory.

## Key findings

- Hydrogen adatoms create flatband states increasing the density of states.
- Hydrogen-related phonon modes enhance electron-phonon coupling.
- Hydrogenation raises the critical temperature of monolayer MgB$_2$ to 67 K, surpassable with strain.

## Abstract

Hydrogen-based compounds under ultra-high pressure, such as the polyhydrides H$_3$S and LaH$_{10}$, superconduct through the conventional electron-phonon coupling mechanism to attain the record critical temperatures known to date. We demonstrate here that the intrinsic advantages of hydrogen for phonon-mediated superconductivity can be exploited in a completely different system, namely two-dimensional (2D) materials. We find that hydrogen adatoms can strongly enhance superconductivity in 2D materials due to flatband states originating from atomic-like hydrogen orbitals, with a resulting high density of states, and due to the emergence of high-frequency hydrogen-related phonon modes that boost the electron-phonon coupling. As a concrete example, we investigate the effect of hydrogen adatoms on the superconducting properties of monolayer MgB$_2$, by solving the fully anisotropic Eliashberg equations, in conjunction with a first-principles description of the electronic and vibrational states, and the coupling between them. We show that hydrogenation leads to a high critical temperature of 67 K, which can be boosted to over 100 K by biaxial tensile strain.