Prediction of phonon-mediated superconductivity in borophene

Abstract

Superconductivity in two-dimensional compounds is widely studied, not only because of its application in constructing nano-superconducting devices, but also for general scientific interest. Very recently, borophene (a two-dimensional boron sheet) has been successfully grown on the Ag(111) surface, through direct evaporation of a pure boron source. The experiment unveiled two types of borophene structures, namely ${\ensuremath{\beta}}_{12}$ and ${\ensuremath{\chi}}_{3}$. Herein, we employed density-functional first-principles calculations to investigate the electron-phonon coupling and superconductivity in both structures of borophene. The band structures of ${\ensuremath{\beta}}_{12}$ and ${\ensuremath{\chi}}_{3}$ borophenes exhibit inherent metallicity. We found that electron-phonon coupling constants in the two compounds are larger than that in ${\mathrm{MgB}}_{2}$. The superconducting transition temperatures were determined to be 18.7 K and 24.7 K through the McMillian-Allen-Dynes formula. These temperatures are much higher than the theoretically predicted 8.1 K and experimentally observed 7.4 K superconductivity in graphene. Our findings will enrich nano-superconducting device applications and boron-related materials science.