Thermal difference reflection spectroscopy of high {Tc} superconductors

The temperature dependent thermal difference reflectance (TDR) spectra of thin film samples of Tl{sub 2}Ba{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10}, (BiPb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10}, Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8} and YBa{sub 2}Cu{sub 3}O{sub 7} have been measured for photon energies between 0.3 and 4.5 eV at temperatures above and below each material`s superconducting critical temperature. The amplitude of the characteristic optical structure near the screened plasma frequency of each sample in the normal state TDR spectrum varies approximately linearly with temperature, T, indicating that the temperature dependent optical scattering rate in these materials scales with temperature as T{sup 2}. From the TDR spectra collected above and below the critical temperature of each sample, the superconducting to normal state reflectance ratio, R{sub S}/R{sub N}, has been obtained. In these materials, a feature exists in the experimental R{sub S}/R{sub N} spectrum at energies between 1.5 and 2.0 eV which can be accounted for by treating the superconductivity in an Eliashberg model with a coupling function that includes both an electron-phonon interaction and a high energy electron-boson interaction located between 1.6 and 2.1 eV. Good agreement is obtained between theory and experiment based upon this description of the superconducting state.