Pinball liquid phase from Hund's coupling in frustrated transition-metal oxides

Abstract

The interplay of nonlocal Coulomb repulsion and Hund's coupling in the d-orbital manifold in frustrated triangular lattices is analyzed by a multiband extended Hubbard model. We find a rich phase diagram with several competing phases, including a robust pinball liquid phase, which is an unconventional metal characterized by threefold charge order, bad metallic behavior, and the emergence of high-spin local moments. Our results naturally explain the anomalous charge-ordered metallic state observed in the triangular layered compound AgNiO 2 . The potential relevance to other triangular transition-metal oxides is discussed.

Noncollinear and noncoplanar magnetic order in the extended Hubbard model on anisotropic triangular lattice

“…For a certain range of parameter values, one of the sublattice is magnetic while the other is nonmagnetic. This highly resembles the pinball-liquid state reported in theoretical studies of multiband extended Hubbard model on triangular lattice [21][22][23][24] . The phase diagrams presented here set the stage for further studies to analyze the stability of these phases.…”

“…The influence of nearest neighbor Coulomb repulsion on these phases is also investigated. We find that a pinball-liquid like charge ordering phase, which has so far been reported in spinless fermion models or multiorbital models on triangular lattice [21][22][23][24] , is stabilized by the Coulomb interactions at a filling fraction of n = 2/3 and occurs concomitantly with either collinear or noncollinear magnetic order. Given the fundamental nature of the Hubbard Hamiltonian, our results are of general interest.…”

Doping-driven metal-insulator transitions and charge orderings in the extended Hubbard model

“…This state is characterized by quasilocalized charges coexisting with more itinerant electrons, which gives rise to strong quasi-particles renormalization with a mechanism analogous to the heavy fermion compounds 49 . In the multi-orbital case 56 , which is relevant for transition-metal oxides, the onset of a pinball phase has been associated to the a finite value of the Hund's exchange 57 .…”

Multiorbital kinetic effects on charge ordering of frustrated electrons on the triangular lattice

“…The method is free from local constraints and ad hoc symmetrizations of the solution; that is, no particular form of the ground state is assumed. This allows us to obtain the most general ordered states of the model in an unbiased way and has been proven very successful in predicting novel phases in related models 24,34 . Also due to the absence of constraints, the resulting mean-field Hamiltonian does not necessarily commute with τ 2 and τ z , which are, respectively, the total orbital pseudospin operator and its z component.…”

“…Finally, multiband effects on charge ordering on the triangular lattice have been studied via both UHF and dynamical mean-field theory in Ref. [24], but only the fully isotropic limit t = t was explored.…”