Strong Electron-Phonon Coupling and Multiband Superconductivity in Hexagonal BP3 Monolayer

We investigate the structural, electronic, and superconducting properties of a hexagonal BP3 monolayer using first-principles calculations combined with anisotropic Migdal-Eliashberg theory. The optimized structure exhibits a stable, slightly buckled configuration, as confirmed by phonon dispersion analysis and ab initio molecular dynamics simulations. The phonon spectrum indicates high-frequency vibrational modes associated with B-P bonding. Electronic band structure calculations reveal a multiband metallic state, with states near the Fermi level predominantly derived from pz orbitals of both boron and phosphorus atoms, forming two distinct Fermi surface sheets. The electron-phonon coupling is relatively strong, with a total coupling constant of lambda = 1.59, dominated by low- and intermediate-frequency phonon modes. Solving the anisotropic Migdal-Eliashberg equations yields a superconducting transition temperature of Tc = 9.7 K. The superconducting state is characterized by a nodeless but anisotropic gap structure, exhibiting two distinct gap values of approximately 2.25 and 1.74 meV associated with different Fermi surface sheets. These results identify the BP3 monolayer as a strongly coupled, multiband two-dimensional superconductor and provide insight into the role of orbital hybridization in electron-phonon-mediated superconductivity in low-dimensional systems.