Title: PSEUDOSPIN-ELECTRON MODEL AT WEAK COUPLING
Author(s): I.V.Stasyuk, T.S.Mysakovych (Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine)

The static and dynamic dielectric susceptibility of the pseudospin-electron model is investigated in the random phase approximation. The possibility of the phase transition to the homogeneous phase, to the phase with doubly modulated lattice period and to the incommensurate phase is revealed in the regime $\mu=\mathrm{const}$ depending on the value of the chemical potential. The phase separation on the homogeneous and phase with doubly modulated lattice period is established and the phase diagrams $(n,h)$ are built. The influence of the tunnelling-like splitting on the phase transition picture is studied. The presence of pseudospin-wave excitations and the smooth excitation spectrum and the possibility of their superimposing are revealed.

Key words: pseudospin-electron model, phase transitions, excitation spectrum
PACS: 63.20.Ry, 64.70.Kb, 71.10.Fd, 77.80.Bh