An Optical Investigation of Electronic Excitations in the High-Temperature Superconductors YBa2Cu307 _ 6 and Bi2Sr2CaCu2O8 + Δ

The results of Raman scattering from superconducting gap excitations in the high T_c compounds YBa₂Cu₃O_7-δ and Bi₂Sr₂CaCu₂O_8+Δ are compared. In the normal state, both materials exhibit strong electronic interband scattering which manifests itself as a broad background continuum having both A_1g and B_1g symmetry components. At low temperatures a redistribution of this electronic scattering occurs, indicative of the formation of a superconducting gap in these compounds. The two symmetries exhibit distinct redistribution, however, denoting strong anisotropy. At temperatures well below T_c, both compounds exhibit residual low-energy scattering, a feature suggestive of the coexistence of normal electrons and superconducting quasi-particles.