The mid-infrared dielectric function of NBCO in the a-b plane from 85 K to 300 K

Results are reported on the a-b plane dielectric function (epsilon) of thin-film c-axis NdBa2Cu3O7-d with close to optimal O doping (Tc approx equals 90 K) in the mid-ir (wavelength 3.392 mu m) at 85-300 K. An attenuated total reflectance technique based on the excitation of surface plasmon polaritons is used. Results show that epsilonr decreases quasi-linearly with increasing temperature, while epsiloni is invariant with temperature to within experimental uncertainties. Representative values are epsilon = [epsilonr + iepsiloni] = (-12.9plus/minus 0.6) + i(23.0plus/minus 1.5) at T approx equals 295 K and epsilon = (-15.7plus/minus 0.7) + i(23.5plus/minus 1.1) at T approx equals 90 K. The raw data are interpreted in terms of the generalized Drude model which gives effective scattering rates (1/t*) that increase with temperature from about 3800 cm-1 at 90 K to about 4300 cm-1 at 295 K. 44 refs.