Raman properties intrinsic to superconductivity in the Bi-Sr-Ca-Cu-O system

Previous Raman studies of the Bi-Sr-Ca-Cu-O system have provided an abundance of interesting results including the existence of an electronic continuum which redistributes below $T_c$, an anomalous phonon renormalization effect, and Fano antiresonance behavior of the 290-${\mathrm{cm}}^{\mathrm{-}1}$ vibrational mode. We attempt in this paper to determine what connection these features may have to the superconducting behavior of this compound. In order to draw such conclusions a systematic study has been carried out on numerous ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_{8+\mathrm{\Delta }}$ samples. Our Raman investigations indicate that it is the continuum redistribution and a linear low-energy contribution to the scattering intensity at temperatures T≪$T_c$ that are intrinsic to superconductivity in this system.