Charge Orderings and Phase Separations in Itinerant Fermion Systems at Half Filling

Abstract

We analyse the ground state phase diagrams of the charge orderings in narrow band materials using two eective models: (1) the spinless fermion model (t−W ) with repulsive intersite interaction (Wij > 0) and (2) the molecular crystal model with the coupling of electrons to intramolecular (crystal eld) vibrations. We present results for the case of half lled bands for d = 2 square lattice. The calculations are performed within the (broken symmetry) Hartree-Fock approximation. The study takes into consideration the eects of frustrating next-nearest--neighbour hopping (t2) on the charge ordered states in these systems. We focus on the two cases: (i) homogeneous phases and phase separations involving checkerboard charge ordering with the nesting vector Q = (π, π) only and (ii) homogeneous phases and phase separations involving two types of charge ordering: (a) checkerboard charge ordering with the nesting vector Q = (π, π), and (b) collinear (CL) charge ordering with Q = (0, π) or Q = (π, 0).

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

“…For U = 0 (W > 0) the model (2) is solved using a standard broken-symmetry Hartree-Fock approximation. The mean-field Hamiltonian is diagonalized by means of a Bogoliubov transformation 30,33,[62][63][64][65][66][67][68] . The resulting selfconsistent equations for the total occupation n and the charge polarization ∆ = 1 2 (n A −n B ) are:…”

Effects of Frustrating Hopping on Charge Ordered States in Itinerant Fermion Systems for Arbitrary Concentration in 2D Lattice

“…More detailed discussion of the case of PS involving not only two-sublattice CO but also collinear CO for arbitrary concentration and T ̸ = 0 will be given elsewhere [17].…”

“…The CO phenomena in narrow band materials can be explained on the bases of two main mechanisms: electron correlations and electron-lattice couplings. Here, as in our recent papers [12,15,16] we study this subject using the following two eective models: (i) model of correlated electrons the so-called tW model of spinless fermions with repulsive intersite interaction W [12,16] and (ii) a model of electron-lattice interactions the molecular crystal (MC) model in the static limit, with electrons coupled to intramolecular (crystal eld) vibrations [15,16].…”

“…The model Hamiltonians have the following form: (i) the tW model with intersite density interaction [12,14,16]…”

“…We have performed extensive studies of both models for arbitrary concentrations [17]. Below we only shortly summarize the main ndings presenting selected nite temperature phase diagrams which have been evaluated at arbitrary concentration, by comparing the free energies of the homogeneous phases (CO, NO) and the PS states.…”