RAMAN-SCATTERING IN A CORRELATED SUPERCONDUCTOR .2. A FINITE-TEMPERATURE STUDY

The temperature dependence of the Raman spectrum of copper oxide super conductors is calculated assuming that the normal state of these syste ms is a correlated metal and that the superconductivity arises due to the correlation bag mechanism proposed earlier (Debanand Sa, S.N. Behe ra (1992), here after referred to as 1). The correlated metallic state is characterized by the presence of a strong interaction between the doped charge carriers and the quanta of fluctuations of the pre-existi ng resonating valence bonds in the normal state. It is shown that the presence of such an interaction can give rise to the marginal Fermi li quid behaviour, which follows from the pair polarisability function. T he model therefore, successfully explains the constant intensity backg round observed in the Raman spectrum due to the scattering by the char ge carriers. In order to understand the observed temperature dependent shift and change in width of the phonons, their spectral density func tions are calculated. Two different kinds of interaction between the c harge carriers and phonons were derived in I, i.e. (i) the usual elect ron-phonon interaction where a phonon decays by exciting an electron-h ole pair and (ii) the other where the decay process involves a quasi-p article pair. It was postulated that the localised phonons couple to t he charge carrier by the later process whereas the propagating ones in teract by the former. The temperature dependence of the phonon self-en ergies due to the two processes is calculated and the spectral density functions are computed. The calculated temperature dependent shift an d change in width of the phonons show qualitative agreement with the o bserved result.