Dielectric instabilities and phase transitions in pseudospin-electron model of HTSC systems

The possible dielectric instabilities and phase transitions in high-Tc superconductors are analyzed within the pseudospin-electron model involving Hubbard type electron correlations as well as their interaction with local anharmonic vibrational modes. The calculation of the dynamic dielectric susceptibility χ(ω,q) is performed in the generalized random phase approximation. The instabilities with respect to the polarization and/or charge fluctuations are obtained from the temperature dependences of χ(ω,q). The behavior of low-frequency modes in the vicinity of these instabilities is investigated. The case of the infinity narrow electron band is considered in details.