ON THE FROHLICH CHARGE-DENSITY-WAVE AND PEIERLS TRANSITION

The exact solution of the system of nonlinear equations for Frohlich c harge density wave (CDW) in the continuum approximation is discussed, and the temperature behaviour of the CDW condensate is investigated in a framework of the mean-field approximation. It is shown that the CDW representation in the form of a conventional harmonic wave is only co rrect under certain conditions, namely, not too strong an electron-pho non interaction or not too low an electron density. According to the e xact solution, the CDW is essentially a nonlinear wave represented by a harmonic series. This is confirmed by the experimental data on the C DW current oscillation spectra in which the overtones are present toge ther with the principal harmonic (the so called ''narrow band noise'') . At strong enough electron-phonon coupling or at low enough electron density the CDW wave vector is temperature dependent, and the BCS rela tion between Peierls transition temperature and energetic gap in the e lectron spectra at zero temperature is violated.