Uncovering the gap, Δ(ω): Measurement of the Re(σS/σN) in superconducting Tl2Ba2CaCu2O8

Abstract We report measurements of both the normal-state reflectance and the superconducting- to normal-state reflectance ratio of a thin film sample of Tl 2 Ba 2 CaCu 2 O 8 at near-normal incidence for photon energies between 0.09 and 4.5 eV. From these data we have obtained the real part of the superconducting- to normal-state optical conductivity ratio, Re(σ S /σ N ). This quantity can be related directly to structure in Δ(ω) without the need to invoke Eliashberg theory. We find structure in Δ(ω) for superconducting Tl 2 Ba 2 CaCu 2 O 8 at low-energy, presumably due to electron-phonon coupling, and additional structure at approximately 1.2 eV and 1.7eV which we attribute to an electronic component of the pairing interaction in this material.