Predicting multiple Dirac-cones and ultrahigh Fermi velocity in perovskite Rc phase LaCuO3

Abstract

Three-dimensional (3D) Dirac semimetal as an intermediate between a trivial insulator and topological insulator has generated much attention, yet there are currently very few experimental studies. In this study, on the basis of density functional theory calculations and a theoretical tight-binding model, we have predicted that the experimentally synthesised LaCuO₃ compound (Rc phase) possesses multiple Dirac cones in its electronic structure. The bands are linearly dispersed, and the compound exhibits comparable Fermi velocity (0.92 × 10⁶ m s⁻¹) to that of graphene; also, the bands possess large regions of linear dispersion. More interestingly, rings of Dirac nodes formed by multiple Dirac points and a distorted Dirac cone coexist in the LaCuO₃ compound. The Dirac states in LaCuO₃ are protected by the D_3d symmetry, with dominant contributions from the d orbitals of Cu and p orbital of O. The particular space groups allow 3D Dirac points as symmetry-protected degeneracies. Thus, there are probably numerous 3D Dirac semimetals in the perovskite (Rc) phase yet to be discovered.