Prediction of phonon-mediated superconductivity in borophene

Superconductivity in two-dimensional compounds is widely concerned, not only due to its application in constructing nano-superconducting devices, but also for the general scientific interests. Very recently, borophene (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 $\beta_{12}$ and $\chi_3$. 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 $\beta_{12}$ and $\chi_3$ borophenes exhibit inherent metallicity. We found electron-phonon coupling constants in the two compounds are larger than that in MgB$_2$. The superconducting transition temperatures were determined to be 18.7 K and 24.7 K through McMillian-Allen-Dynes formula. These temperatures are much higher than theoretically predicted 8.1 K and experimentally observed 7.4 K superconductivity in graphene. Our findings will enrich the nano-superconducting device applications and boron-related material science.