High Transition Temperature Driven by Type-II Dirac Fermions in Topological Superconductor BBeB Nanosheet.

Topological superconductors (TSCs) offer a promising avenue for delving into exotic states of matter and fundamental physics. We propose a strategy for realizing high transition temperatures (high-) in TSCs by leveraging nontrivial topology alongside a high carrier density near the Fermi level in metal-doped borophenes. We identified 39 candidates with exceptional thermodynamic stability from thousands of Be-intercalated borophenes (BeB) via extensive structural searches. Seven candidates exhibit high carrier densities, with BBeB emerging as a particularly promising candidate. This nanosheet displays both type-I and type-II Dirac fermions, indicative of topological metals, thereby positioning it as an ideal platform for high- TSCs. The high-density π electrons of BBeB originating from type-II Dirac fermions, coupled with the out-of-plane vibrations of B and Be atoms, significantly enhance the electron-phonon coupling (λ = 1.42), resulting in a substantially high- of 31.5 K. These findings underscore the potential of metal-doped borophenes as a cutting-edge material platform for achieving high- TSCs.