Charge ordering and phase separation in the infinite dimensional extended Hubbard model

Abstract

We study the extended Hubbard model with both on-site (U) and nearest neighbor (V) Coulomb repulsion using the exact diagonalization method within the dynamical mean field theory. For a fixed U (U=2.0), the T-n phase diagrams are obtained for V=1.4 and V=1.2, at which the ground state of n=1/2 system is charge-ordered and charge-disordered, respectively. In both cases, robust charge order is found at finite temperature and in an extended filling regime around n=1/2. The order parameter changes nonmonotonously with temperature. For V=1.4, phase separation between charge-ordered and charge-disordered phases is observed in the low temperature and n<0.5 regime. It is described by an "S"-shaped structure of the n-μ curve. For V =1.2, the ground state is charge-disordered, and a reentrant charge-ordering transition is observed for 0.42<n<0.68. The relevance of our results to experiments for doped manganites is discussed.