Experimental studies of the high-temperature superconducting cuprates using thermal difference reflectance spectroscopy

摘要

Abstract: We have previously measured the temperature dependent thermal difference reflectance (TDR) spectra of several high-temperature superconducting thin films. From the TDR spectra collected above and below the critical temperature of each sample, the superconducting to normal state reflectance ratio, R$-S$/R$-N$/, has been obtained. We observe significant deviations from unity in this reflectance ratio at photon energies on the order of 2.0 eV. Both the temperature dependence and location of this structure in the R$-S$//R$-N$/ spectra may be described by solving the Eliashberg integral equations with an electron-boson coupling function that includes both an electron-phonon interaction and an interaction located at approximately the energies of known charge transfer excitations in these materials (approximately 2.0 eV). We found remarkably good agreement between the experimental data and the results of our calculations based upon this description of the superconducting state. We also use the technique of TDR spectroscopy to probe the superconducting proximity effect. By measuring the TDR spectra of the silver layer in a Ag-(BiPb)$-2$/Sr$-2$/Ca$-2$/Cu$-3$/O$- 10$/ bi-layer junction or the indium layer in a In-Ag-(BiPb)$-2$/Sr$-2$/Ca$-2$/Cu$-3$/O$- 10$/ tri-layer junction, at temperatures above and below the critical temperature of the high temperature superconductor, we hope to observe structure due to a proximity induced gap function in the normal metal. !20