Modern Approach to Optical Absorption in Cuprate Superconductors

Adopting the many body quantum dynamical theory of phonon Green’s functions via a general Hamiltonian which includes the effects of electron-phonon interactions, anharmonicities and impurities (but not those of BCS terms) the theory of infrared (i.r.) absorption has been investigated which separates out into (i) diagonal and (ii) non-diagonal contributions. The non-diagonal contribution emerges only in the impure crystals and becomes extinct in pure crystals. The critical investigations divulges that the infrared (i.r.) absorption coefficients not only depends upon electron-phonon coupling coefficient but also on temperature, which appears as the unique feature of the present theory and provide us a plat form to study a system in superconducting and normal regions. The Y B a 2 C u 3 O 7− δ superconductor has been taken for the purpose of analysis and comparison with the well-established experimental results.