Superconductivity-induced optical changes for energies of 100 Delta in thecuprates - art. no. 224514

We present information on the temperature-dependent changes of the complex pseudodielectric function in the high-T-c superconductor Bi2Sr2CaCu2O8-delt a by means of spectroscopic ellipsometry. We reveal the existence of three distinct spectral regions. Below 2 eV, there are changes in the dielectric function associated with the free-carrier response. In slightly underdoped compounds we find at around 3 eV a strong rise of epsilon (2) below the tem perature signifying the opening of a pseudogap (T* approximate to 150 K) an d an additional enhancement of similar strength below the superconducting t ransition(T-c=90 K). With overdoping, we find vanishing effects above T-c a nd a significant decrease in the T-c related effect. This behavior fits to the strong suppression of the antiferromagnetic correlations with increasin g doping.