Superconductivity-induced optical changes for energies of 100Δ in the cuprates -: art. no. 224514

We present information on the temperature-dependent changes of the complex pseudodielectric function in the high-T-c superconductor Bi2Sr2CaCu2O8-delta 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 temperature signifying the opening of a pseudogap (T* approximate to 150 K) and an additional enhancement of similar strength below the superconducting transition(T-c=90 K). With overdoping, we find vanishing effects above T-c and a significant decrease in the T-c related effect. This behavior fits to the strong suppression of the antiferromagnetic correlations with increasing doping.