Two-gap-like anisotropic superconductivity in a bulk boron kagome lattice

Abstract

Since a report of superconductivity in elemental boron at high pressure [M. I. Eremets et al., Science, 2001, 293, 272–274], many efforts have been devoted to the search for superconductivity in diverse boron allotropes. However, there are few superconducting phenomena to be discovered theoretically and experimentally in elemental bulk boron crystals at normal pressure to date. In this paper, we propose a metastable but dynamically stable metallic bulk boron phase within the kagome lattice, and demonstrate from first principles good superconductivity with a high superconducting critical temperature T_c, e.g., ∼34–39 K, in the elemental bulk boron at ambient pressure. Our calculations indicate that such a high-T_c superconductivity is closely related to the Fermi surface displaying strong electron–phonon coupling with a two-region-like distribution feature, which resulted from two different types of covalent bonding crossing the Fermi level and also gives rise to a two-gap-like superconducting nature in the system. We uncover that the strong electron-lattice coupling is dominated by the transversal acoustic phonon modes around a degenerate softening kink that places the system on the verge of a latent charge density wave. The present findings shed light on a study of the high-T_c superconductivity of the elemental bulk boron phase at normal pressure.