The mid-infrared dielectric function of NBCO in thea-bplane from 85 K to 300 K

Abstract

Results are reported on the a-b plane dielectric function (ε) of thin-film c-axis NdBa2Cu3O7-δ with close to optimal oxygen doping (Tc~90 K) in the mid-infrared (wavelength 3.392 µm) over the temperature range 85 K to 300 K. An attenuated total reflectance technique based on the excitation of surface plasmon polaritons is used. The results show that |εr| decreases quasi-linearly with increasing temperature, while εi is invariant with temperature to within experimental uncertainties. Representative values are ε = [εr + iεi] = (-12.9±0.6) + i(23.0±1.5) at T~295 K and ε = (-15.7±0.7) + i(23.5±1.1) at T~90 K. The raw data are interpreted in terms of the generalized Drude model which gives effective scattering rates (1/τ*) that increase with temperature from about 3800 cm-1 at 90 K to about 4300 cm-1 at 295 K. There are indications of a superlinear T-dependence in the scattering, 1/τ*; a fit to a function of the form 1/τ* = A + BTα gives α = 2.8±0.7. The effective plasma frequency, ωp*, with an average value of approximately 21 000 cm-1 was independent of temperature.