Raman scattering from superconducting gap excitations in Tl2Ca2Ba2Cu3O10 single crystals

Raman spectra taken from several well-characterized superconducting Tl2Ca2Ba2Cu3O10 (2:2:2:3) single crystals (Tc=105 K) display the characteristic phonon spectrum of the 2:2:2:3 phase on top of a broad background continuum interpreted as electronic scattering. The electronic scattering continuum decreases substantially below Tc for frequency shifts of smaller than 400 cm-1, indicating the formation of a superconducting gap. The gap does not show the expected abrupt onset but a linearly rising electronic scattering background similar to observations in YBa2Cu3O7, possibly indicating a distribution of gaps or the presence of electronic excitations within the gap. © 1989 The American Physical Society.