High Transition\nTemperature Driven by Type-II Dirac\nFermions in Topological Superconductor B<sub>7</sub>Be<sub>2</sub>B<sub>7</sub> Nanosheet

Topological superconductors (TSCs)\noffer a promising\navenue for\ndelving into exotic states of matter and fundamental physics. We propose\na strategy for realizing high transition temperatures (high-<i>T</i><sub>c</sub>) in TSCs by leveraging nontrivial topology\nalongside a high carrier density near the Fermi level in metal-doped\nborophenes. We identified 39 candidates with exceptional thermodynamic\nstability from thousands of Be-intercalated borophenes (Be<sub>1–<i>x</i></sub>B<sub><i>x</i></sub>) via extensive structural\nsearches. Seven candidates exhibit high carrier densities, with B<sub>7</sub>Be<sub>2</sub>B<sub>7</sub> emerging as a particularly promising\ncandidate. This nanosheet displays both type-I and type-II Dirac fermions,\nindicative of Z2 topological metals, thereby positioning\nit as an ideal platform for high-<i>T</i><sub>c</sub> TSCs.\nThe high-density π electrons of B<sub>7</sub>Be<sub>2</sub>B<sub>7</sub> originating from type-II Dirac fermions, coupled with the\nout-of-plane vibrations of B and Be atoms, significantly enhance the\nelectron–phonon coupling (λ = 1.42), resulting in a substantially\nhigh-<i>T</i><sub>c</sub> of 31.5 K. These findings underscore\nthe potential of metal-doped borophenes as a cutting-edge material\nplatform for achieving high-<i>T</i><sub>c</sub> TSCs.