OPTICAL-PROPERTIES OF YBA2CU3O7-DELTA THIN-FILMS

Temperature-dependent reflectance and transmittance measurements (1250 -8000 cm(-1)) of thin Y-Ba-Cu-O films are reported and the complex die lectric response epsilon(omega) is directly determined from the measur ed data. We find that epsilon(omega) is more complex than predicted by any of the existing models, in particular the marginal and the nested Fermi liquids, as well as the two-component approach (Drude and midin frared terms). A phenomenological analysis reveals either a two-fluid or a complicated one-fluid model, which is yet to be explained theoret ically. The near-infrared (NIR) transmittance is weakly temperature de pendent in the normal state, but almost temperature independent in the superconducting state; Both the normal and the superconducting states are anomalous and non-Fermi-liquid-like with renormalization of energ ies much higher than any superconducting energy gap. Such observations have previously been reported only in powder absorbance measurements but not in single-crystal and thick-film reflectance data. We present a quantitative analysis in which the powder absorbance results are rec overed from thin-film data. The NIR response is argued to be of crucia l importance for the understanding of the high-temperature superconduc tors in both the normal and the superconducting states.