OPTICAL EVIDENCE OF POLARONS IN SUPERCONDUCTING CUPRATES

The reflectivity R(omega) of h-doped, metallic Bi2Sr2CuO6, as well as that of e-doped Nd(Gd)(2-x)CexCuO4-y, shows local modes in the far-inf rared as well as a broad absorption centered at similar to 1000 cm(-1) (d-band). The d-band is made up by intense overtones of the local mod es, thus revealing its polaronic origin. In the metallic samples, the polaronic absorption is superimposed to a Drude term. The intensity of the d-band is shown to be correlated with the optimum critical temper ature of the corresponding cuprate family.