Topological properties after light ion irradiation on Weyl semimetal niobium phosphide from first principles

Abstract

A member of the nonmagnetic Weyl semimetal family, niobium phosphide (NbP), is a new low-energy dissipative material due to the properties of its nontrivial energy band structure and topologically protected nodes. This paper mainly focus on the changes of the topological properties of the crystal NbP after H and He ions irradiation, a novel research view. In order to demonstrate the formation process of doping defects, we use TD-DFT to simulate the whole path of H ion passing the bulk NbP, while both the total energy change for system and the radial drag force as a function of the projectile position are investigated. The energy band structures and density of states for the equilibrium point defect have been analyzed by means of the DFT method based on the CASTEP package. A strikingly phenomenon discovered is that diverse kinds of defects are able to modify the symmetrically protected Weyl points to some extent. Specifically, when H or He as an interstitial particle in the crystal NbP, the degenerate bands are uncoupled; meanwhile, the Fermi levels are shifted upward 0.12 eV and 0.18 eV, respectively. In contrast to the defect structures formed by P, the defects caused by Nb present the greater destructive power to the Weyl points. By contrast, the calculations of formation energy have demonstrated that H substitute for Nb is the most easily formed defect structure, and the defect with interstitial H atom is most stable structure within the scope of this research.