Models of Reentrant Charge Ordering in Manganites

Recently, a melting of the charge ordered state on decreasing the temperature, i.e. reentrant behavior, has been found in Pr_0.65(Ca_0.7Sr_0.3)_0.35MnO₃ and in LaSr₂Mn₂O₇. The following theoretical models of reentrant charge ordering in the above manganites are considered: i) the square lattice extended Hubbard model with both on-site and nearest neighbor Coulomb repulsion, ii) the extended double exchange model, where the reentrant charge ordering appears due to the dependence of the hopping on the temperature resulting from double exchange.