Raman scattering in a correlated superconductor II. A finite temperature study☆
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Abstract:

AbstractThe temperature dependence of the Raman spectrum of copper oxide superconductors is calculated assuming that the normal state of these systems is a correlated metal and that the superconductivity arises due to the correlation bag mechanism proposed earlier (Debanand Sa, S.N. Behera (1992), here after referred to as I). 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-existing resonating valence bonds in the normal state. It is shown that the presence of such an interaction can give rise to the marginal Fermi liquid behaviour, which follows from the pair polarisability function. The model therefore, successfully explains the constant intensity background observed in the Raman spectrum due to the scattering by the charge carriers. In order to understand the observed temperature dependent shift and change in width of the phonons, their spectral density functions are calculated. Two different kinds of interaction between the charge carriers and phonons were derived in I, i.e. (i) the usual electron-phonon interaction where a phonon decays by exciting an electron-hole pair and (ii) the other where the decay process involves a quasi-particle pair. It was postulated that the localised phonons couple to the charge carrier by the later process whereas the propagating ones interact by the former. The temperature dependence of the phonon self-energies due to the two processes is calculated and the spectral density functions are computed. The calculated temperature dependent shift and change in width of the phonons show qualitative agreement with the observed result.

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