# Electron-phonon coupling in a honeycomb borophene grown on Al(111) surface

## TL;DR

This study investigates the electronic structure and electron-phonon interactions in honeycomb borophene on Al(111), predicting potential superconductivity around 6.5 K based on first-principles calculations.

## Contribution

It provides the first detailed analysis of electron-phonon coupling in honeycomb borophene on Al(111), highlighting substrate effects and predicting superconductivity in Al-decorated borophene.

## Key findings

- Honeycomb borophene exhibits metallized $\sigma$-bonding bands due to charge transfer.
- Electron-phonon coupling is weaker than in MgB$_2$ because of phonon mode hardening.
- Interlayer coupling with Al phonons suggests possible superconductivity around 6.5 K.

## Abstract

Recently, a honeycomb borophene was reported to grow successfully on Al(111) surface. Since the metallic $\sigma$-bonding bands of honeycomb boron sheet play a crucial role in the 39 K superconductivity of MgB$_2$, it is physically interesting to examine whether similar property exists in this material. We have calculated the electronic structures and the electron-phonon coupling for honeycomb borophene by explicitly considering the substrate effect using first-principles density functional theory in conjunction with the Wannier interpolation technique. We find that the $sp^2$-hybridized $\sigma$-bonding bands of honeycomb borophene are metallized due to moderate charge transfer from the Al substrate, similar as in MgB$_2$. However, the electron-phonon coupling in honeycomb borophene is much weaker than in MgB$_2$ due to the hardening of the bond-stretching boron phonon modes and the reduction of phonon density of states. Nevertheless, the interlayer coupling between Al-associated phonons and electrons in borophene is strong. Based on this observation, we predict that a 6.5 K superconducting transition can be observed in a free-standing borophene decorated by a single Al layer, namely monolayer AlB$_2$. Accordingly, similar superconducting transition temperature could be expected in honeycomb borophene on Al(111).