Prediction of superconductivity in bilayer borophenes

Borophenes and related two-dimensional materials have exhibited many exotic properties, especially for superconductivity, although the superconductivity of single-layer borophene is suppressed by the strains or doping from its substrates. Intriguingly, bilayer (BL) borophenes can be stabilized by appropriate pillar density and hexagonal holes density, rather than being supported by Ag(111) or Cu(111) substrates. Thus, we studied the two most stable structures, namely BL-B8 and BL-B30, stabilized by the above-mentioned two methods. Within density functional theory and Bardeen-Cooper-Schrieffer theory framework, their stability, electron structures, and phonon properties, as well as possible superconductivity are systematically scrutinized. The metallic BL-B8 and BL-B30 exhibit intrinsic superconducting features with superconductivity transition temperatures (T-c) of 11.9 and 4.9 K, respectively. The low frequency (below 400 cm(-1)) consisting of out-of-plane vibrations of boron atoms plays crucial rule in their superconductivity. In particular, a Kohn anomaly appears at the Gamma point in BL-B8, leading to substantial electron-phonon coupling. Here, our findings will provide instructive clues for experimentally determining the superconductivity of borophene and will broaden the two-dimensional superconductor family.

Automated summary

Borophenes and related two-dimensional materials exhibit exotic properties, with bilayer borophenes BL-B8 and BL-B30 showing intrinsic superconducting features with transition temperatures of 11.9 K and 4.9 K, respectively. The low-frequency vibrations of boron atoms play a crucial role in their superconductivity, with notable electron-phonon coupling observed in BL-B8. These findings provide guidance for experimentally determining the superconductivity of borophene and expanding the two-dimensional superconductor family.