Anisotropic Superconductivity in Bilayer Kagome Borophene.

Abstract

The unique electron configuration of boron allows it to form a rich variety of allotropes and exhibits great potential for superconductors. In this work, the superconductivity in bilayer Kagome borophene (BK-borophene) is investigated by first-principles calculations. The results show that BK-borophene is an anisotropic superconductor with strong electron-phonon coupling (EPC) and a high critical temperature (T_c) ≈17.4-35.0 K predicted by the anisotropic Migdal-Eliashberg equations and McMillan-Allen-Dynes formula. The superconductivity in BK-borophene is attributed to the strong EPC between electrons near the Fermi level and three phonon modes including the A_2u mode and two E_g modes. The anisotropic superconductivity is due to the anisotropic EPC between the band related to the Dirac-like cone and the flat band. The electronic structure of BK-borophene has the van Hove singularity (VHS) and higher-order van Hove singularity (HOVHS) near the Fermi level, which can lead to the density of states divergence, charge accumulation, and EPC enhanced. The anisotropic EPC indicates that the HOVHS on the Dirac-like cone has the larger EPC strength, which may enhance the T_c. All these results indicate that BK-borophene holds great potential for applications in superconductivity. This work may benefit the research on boron-based materials and novel superconductors.