OPTICAL EVIDENCE OF AN ELECTRONIC CONTRIBUTION TO THE PAIRING INTERACTION IN SUPERCONDUCTING TL2BA2CA2CU3O10

We report the results of a study of the temperature-dependent thermal difference reflectance spectra of Tl2Ba2Ca2Cu3O10. At temperatures bel ow T-c, a feature emerges in the spectra with an integrated amplitude that scares as Delta(0)(2)(T), where Delta(0)(T) is the temperature-de pendent superconducting gap. The temperature dependence and location o f this feature can be described by an Eliashberg model with a coupling function that includes both an electron-phonon interaction and an int eraction located at similar to 1.6 eV. We find remarkably good agreeme nt between theory and experiment based upon this description of the su perconducting state.