Abstract

In the old high temperature superconductors, such as Nb₃Sn, Raman measurements have shown that some phonons are strongly renormalized by electrons and that in addition one can observe scattering from gap excitations, as characterized by a peak at a frequency of 2Δ/h, where Δ is the gap parameter. We present and compare the results of Raman scattering from phonons and superconducting gap excitations in the high T_c compounds YBa₂Cu₃0_7−δ.s and Bi₂Sr₂CaCu₂O_8+Δ. In the normal state, both materials exhibit strong electronic interband scattering which manifests itself as a broad background continuum baying both A_1g and B_1g symmetry components. At low temperature there occurs a redistribution of this electronic scattering with the formation of a broad pronounced peak. This may indicate the formation of a superconducting gap in these compounds. The two symmetries exhibit a distinctly different redistribution, however, implying 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 quasiparticles.

© 1989 Optical Society of America