Reentrant charge ordering caused by polaron formation
Abstract
Based on a two-dimensional extended Hubbard model with electron-phonon interaction, we have studied the effect of small polaron formation on the charge ordering (CO) transition. It is found that for fully ferromagnetically ordered spins the CO state may go through a process of appearance, collapse and reappearance with decreasing temperature. This is entirely due to a temperature-dependent polaron bandwidth. On the other hand, when a paramagnetic spin state is considered, only a simple reentrance behaviour of the CO transition is found, which is only partly due to polaron formation. This model is proposed as an explanation of the observed reentrant behavior of the CO transition in the layered manganite LaSr$_2$Mn$_2$O$_7$.Keywords
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