OPTICAL CONDUCTIVITY IN COPPER-OXIDE SUPERCONDUCTORS

Frequency dependent conductivity sigma(omega) is calculated in the fra mework of the asymmetric Hubbard model for copper oxides in the limit of strong coupling, U much greater than t(alpha,beta), where t(alpha,b eta) are hopping integrals. By using the mode coupling approximation r elaxation rates are calculated in the lowest order of t(alpha,beta)/U in terms of spin and charge correlation functions. The Drude relaxatio n is proportional to [(t(alpha,alpha)(2) - t(12)(2))](2) where alpha = 1 or 2 for the singly (d-hole) or doubly (p-d singlet) occupied subba nds. It follows that for hole doped copper oxides the Drude relaxation rate due to spin fluctuations should be much larger then for electron ically doped ones.