MAXIMUM INFORMATION FROM THE SUPERCONDUCTING GAP MEASUREMENTS ON HIGH-T-C MATERIALS

Exploiting the possibility, for all the equilibrium properties, of app roximating the Eliashberg function by a set of two Einstein peaks, we systematically study the spectral and coupling dependence of the ratio Delta/T-c. We give general results for the spectral and coupling depe ndence of the gap ratio, which can be easily exploited for extracting the maximum information from any experimental gap measurement. In the regimes potentially relevant for high-T-c superconductivity the gap ra tio is strongly spectral dependent and our study is fruitful. In cupra tes, our study combined with an analysis of the incompatibility of the infrared gap measurements with the other gap measurements, leads to t he conclusion that the coupling is quite strong and it is concentrated in a region of frequencies of the order of 25-50 meV. The previous in compatibility can be considered as evidence for the relevance of our f ramework in cuprates. The large gap values reported from tunneling exp eriments in fullerides, combined with Raman spectroscopy data, indicat e that at least 90% of the coupling in these materials is concentrated in a low-energy region approximate to 10 meV, the rest being concentr ated in a high-energy region 180-200 meV.