Renormalization of effective interactions in a negative charge transfer insulator

Abstract

We compute from first principles the effective interaction parameters appropriate for a low-energy description of the rare-earth nickelate LuNiO3 involving the partially occupied eg states only. The calculation uses the constrained random-phase approximation and reveals that the effective on-site Coulomb repulsion is strongly reduced by screening effects involving the oxygen-p and nickel-t2g states. The long-range component of the effective low-energy interaction is also found to be sizeable. As a result, the effective on-site interaction between parallel-spin electrons is reduced down to a small negative value. This validates effective low-energy theories of these materials proposed earlier. Electronic structure methods combined with dynamical mean-field theory are used to construct and solve an appropriate low-energy model and explore its phase diagram as a function of the on-site repulsion and Hund's coupling. For the calculated values of these effective interactions we find, in agreement with experiments, that LuNiO3 is a metal without disproportionation of the eg occupancy when considered in its orthorhombic structure, while the monoclinic phase is a disproportionated insulator. arXiv:1707.09820v1 [cond-mat.str-el]

Spectral functions of Sr2IrO4: theory versus experiment

“…No spectral weight is present at the Fermi level (not shown in Fig. 1), consistent with the insulating nature of Sr 2 IrO 4 [5][6][7] . At a binding energy of 0.2 eV, the spectral weight appears first as a circular spot around the X(π, 0) and its equivalent locations (Fig.…”

“…Multi-orbital physics is rather the generic situation in transition metal oxides [3] and even more so in f-electron compounds. Examples include t 2g -systems such as titanates [4] or vanadates [5], or Mn-, Fe-or Ni-based e g -oxides [6]. A notable exception are high-temperature superconducting cuprates, where a single hole in an otherwise completely filled 3d-shell can be dominantly attributed to an orbital of d x 2 −y 2 character, corresponding -in the parent compounds -to a nominally half-filled configuration.…”

Charge disproportionation and site-selective local magnetic moments in the post-perovskite-type Fe2O3 under ultra-high pressures

“…3 to that observed in the rare-earth nickelates (RNiO 3 with R=Sm, Eu, Y, or Lu)[58][59][60][61][62]. In fact, the latter exhibit a site-selective Mott transition, characterized by a two-sublattice symmetry breaking, with formation of site-selective local moments with localized Ni3d magnetic moments and Ni-d-O-p singlet nonmagnetic states.…”

Complex Magnetic Order in Nickelate Slabs

“…In the bulk calculation the period-four order is stable only in a comparatively narrow U range around 2 eV, but we note that a similarly small value of U ∼ 2 eV has recently also been reported from first-principles constrained randomphase approximation studies of the rare-earth nickelates. 43 For the monoclinic structure the DFT+U calculations result in a gapped, insulating ground state with a small, but robust charge disproportionation evident from a ±1% variation in the d-projected charge around the two different Ni sites in bulk as well as truncated slabs with N = 4, 8. The d-projected charge at each site has been calculated using the VASP standard sphere and in SI- Fig.…”