The Thermodynamic Behaviour of Charge-Ordered Crystals

Abstract
The influence is considered of the low lying collective excitations upon thermodynamic behaviour of charge-ordered states. The collective mode is found which provides the instability of this state relative to the Mott state when intra-(I) and intersite (V) interactions of electrons correspond to a repulsion. If I < 0 and is stronger than the intersite repulsion, the collective excitations correspond to the motion of electron pairs. The energy and the specific heat are calculated and the phase diagram is qualitatively discussed as function of the I to V-ratio.