We investigate the structural, electronic, and superconducting properties of a hexagonal ${\mathrm{BP}}_3$ 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 $p_z$ 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 robust superconducting transition temperature ranging from $T_c=9.0$ to 9.7 K for Coulomb pseudopotentials of ${\mu }^{*}=0.13$ and 0.10, respectively. The superconducting state is characterized by a nodeless but anisotropic gap structure, exhibiting two distinct gap values (approximately 2.25 and 1.74 meV at ${\mu }^{*}=0.10$) associated with different Fermi surface sheets. These results identify the ${\mathrm{BP}}_3$ 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.

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• Superconducting gap
• Superconducting phase transition
• Superconductivity
• Transition temperature
• 2-dimensional systems
• Density functional calculations
• Eliashberg theory