Role of correlation and spin-orbit coupling in LuB4: a first principles study

The recent observation of magnetization plateaus in rare-earth metallic tetraborides has drawn considerable attention to this class of materials. In this work, we investigate the electronic structure of one such canonical system, LuB4, using first-principles density functional theory together with Coulomb correlation and spin-orbit coupling (SOC). The electronic band structures show that LuB4 is a nonmagnetic correlated metal with a completely filled 4f shell. The projected density of states (DOS) shows a continuum at the Fermi level (FL), arising mainly from hybridized Lu d and B p orbitals, along with some discrete peaks well separated from the continuum. These peaks arise mainly due to core-level Lu s, p and 4f atomic orbitals. Upon inclusion of SOC, the discrete peak arising due to Lu p is split into two peaks with j = 1/2, j = 3/2 while the peak arising from Lu 4f orbitals splits into two peaks with j = 5/2 and j = 7/2. These peaks will give rise to multiplet structure in core- level X-ray photo-emission spectroscopy and resonant inelastic X-ray scattering. Inclusion of correlation effects pushes the Lu 4f peak away from the FL, while the qualitative features remain intact. The present calculations will lead to an effective low-energy model for future investigation of transport and other properties.