DIELECTRIC INSTABILITIES AND PHASE-TRANSITIONS IN PSEUDOSPIN-ELECTRONMODEL OF HTSC SYSTEMS

The possible dielectric instabilities and phase transitions in high-T- c superconductors are analyzed within the pseudospin-electron model in volving Hubbard type electron correlations as well as their interactio n with local anharmonic vibrational modes. The calculation of the dyna mic dielectric susceptibility chi(omega, q) is performed in the genera lized random phase approximation. The instabilities with respect to th e polarization and/or charge fluctuations are obtained from the temper ature dependences of chi(omega, q). The behavior of low-frequency mode s in the vicinity of these instabilities is investigated. The case of the infinity narrow electron band is considered in details.