f-Orbital based Dirac states in a two-dimensional uranium compound

Abstract

Theoretical evidence of the existence of Dirac cones in two-dimensional UB_4 is provided. Dirac cones are created due to the interaction of strongly localized U anisotropic f-orbitals with the delocalized network of B p-orbitals in a bilayer honeycombed lattice. Spin–orbit coupling splits the relativistic electronic states in the vicinity of the Fermi level creating cone-shaped gaped bands. The contribution of f-orbitals to the formation of dispersive Dirac states is clearly determined with several theoretical approximations. U atom provides the exact amount of charge to stabilize the B sublattices creating a heavy-electron based material with reminiscent properties of graphene. The interplay between f- and p-orbitals of U and B atoms, respectively, is revealed as the origin of the itinerant electronic states, defying the paradox of delocalized electrons in a heavy-electron based material. Computed phonon diagram exhibits decoupled acoustic and optic modes arising from U and B atom vibrations, respectively, with frequencies of acoustic modes rather small as compared to optic modes. The dynamical properties of isoelectronic UAl4 and UGa4 are also analyzed.