Niobium phosphide

Niobium phosphide is classified as a Weyl semimetal^[2][3], characterized by linearly dispersing electronic bands near the Fermi level that intersect at discrete points known as Weyl nodes. These nodes arise as a direct consequence of the material’s non-centrosymmetric crystal structure and strong spin–orbit coupling^[4]. Experimental studies using angle-resolved photoemission spectroscopy (ARPES) have confirmed the existence of topologically protected surface states, known as Fermi arcs, which connect the projections of Weyl nodes with opposite chirality^[5]. The electronic structure gives rise to unusual transport behavior, including extremely large magnetoresistance and high carrier mobility, reflecting the small, compensated electron and hole pockets near the Weyl points and the topological nature of the band structure^[6].

Niobium phosphide forms dark gray crystals of the non-centrosymmetric, tetragonal system, space group I4₁md (No. 109), with cell parameters a = 0.3334 nm, c = 1.1378 nm, Z = 4.^[7][8], the same structure type as other transition-metal monopnictide Weyl semimetals such as TaAs and NbAs. The unit cell contains four formula units, and each niobium atom is coordinated by six phosphorus atoms and vice versa, forming a three-dimensional network of distorted polyhedra ^[4].