Superconducting Gap Excitations in Bi-Sr-Ca-Cu-O Superconductor Observed by Raman Scattering

Raman scattering is measured in the a b plane of the Bi2.2Sr1.8CaCu2O y superconductor. It is found that the electronic Raman scattering appears as a continuum spectrum in both polarized and depolarized scattering and the electronic continuum interferes with some phonon lines. Below T c, the electronic continuum redistributes due to a gap formation and a broad peak appears at about 400 cm-1, which is larger than the expected value 2Δ=209 cm-1 of the BCS-theory.