Seminarium Fizyki Materii Skondensowanej

Various charge-ordered states are relevant to a broad range of materials, e.g. manganites, cuprates, magnetite, doped transition metal compounds (Ti4xVxO7, WO3−x), heavy-fermion systems and organic compounds. The extended Hubbard model is one of the simplest models that captures the interplay between strong correlations and charge-ordering effects. The model can describe the insulator-metal transition between phases with long-range charge-order. We present studies of the model with both (i) on-site interaction U and (ii) intersite density-density interactions between nearest-neighbors W1 and next-nearest-neighbors W2 beyond the standard Hartree-Fock mean-field two-sublattice assumption. Using the dynamical mean-field theory we derived the ground state phase diagram of this model for arbitrary doping. The interplay between local and non-local interactions drives a variety of phase transitions connecting two distinct charge-ordered insulators (i.e., half-filled and quarter-filled), a charge-ordered metal and a Mott insulating phase. We investigate these transitions and the relative stability of the solutions and we show that the two interactions conspire to stabilize the quarter-filled charge-ordered phase. Additionally, we investigate the effects of next-nearest neighbor interactions on phase diagrams of the model in different limits and we show that charge-stripes can occur for repulsive W2>0 for both signs of W1.