High-pressure crystal growth, superconducting properties, and electronic band structure of Nb₂P₅

Orthorhombic (space group: Pnma) Nb₂P₅ is a high-pressure phase that is quenchable to ambient pressure, which could be viewed as zigzag P_∞ chain-inserted NbP₂. We report herein the high-pressure crystal growth of Nb₂P₅ and the discovery of its superconducting transition at T_c ∼ 2.6 K. The electrical resistivity, magnetization, and specific heat capacity measurements on the high-quality crystal unveiled a conventional type-II weakly coupled s-wave nature of the superconductivity, with the upper critical field H_c2(0) ∼ 0.5 T, the electron-phonon coupling strength λ_ep ∼ 0.5-0.8, and the Ginzburg-Landau parameter κ ∼ 100. The ab initio calculations on the electronic band structure unveiled nodal-line structures protected by different symmetries. The one caused by band inversion, for example, on the Γ-X and U-R paths of the Brillouin zone, likely could bring nontrivial topology and hence a possible nontrivial surface state on the surface. The surface states on the (100), (010), and (110) surfaces were also calculated and discussed. The discovery of the phosphorus-rich Nb₂P₅ superconductor would be instructive for the design of more metal phosphide superconductors, which might host unconventional superconductivity or potential technical applications.