σ bands driven high-temperature superconductivity in hydrogenated hexagonal BC₃ monolayer

Material with metallic σ-bonding bands is expected to be a high-temperature superconductor, due to the sensitivity of σ electrons to lattice vibration. Based on the first-principles calculations, electronic structures of hydrogenated BC₃ monolayers (H_n-B₂C₆ with n=1-8) are systematically investigated. At high coverage of hydrogen, the monolayer stabilizes in chair-like sp³-hybridized configurations, leading to the metallization of σ bands, especially in H₇-B₂C₆ and H₈-B₂C₆. This metallicity originates from the electron deficiency of boron, compared with insulating graphane. Utilizing Wannier interpolation, the electron-phonon coupling strengths for metallic phases of H_n-B₂C₆ are determined. As expected, strong couplings are identified between the conducting σ electrons and low-frequency phonon modes. By solving the anisotropic Eliashberg equations, we confirm that H₇-B₂C₆ and H₈-B₂C₆ are single-gap superconductors with critical temperature being 91 K and 87 K, respectively, exceeding the boiling point of liquid nitrogen. Considering that monolayer BC₃ has been synthesized in experiment, our results demonstrate that hydrogenation of two-dimensional BC₃ provides a viable pathway to achieve high-temperature superconductivity at ambient pressure.