Optical conductivity in YBa2Cu3O7-delta thin films

The real and imaginary parts of the optical conductivity sigma(1) + i sigma (2) of partly untwinned YBa2Cu3O7-delta thin films were measured by submill imeter spectroscopy for frequencies from 100 GHz to 1 THz. The frequency de pendence of the conductivity below T-C can be described by a narrow Drude-l ike peak with strongly temperature-dependent relaxation rates, sigma(1)(nu) does not extrapolate to the universal d-wave value at 0 K. Impurity scatte ring significantly different to the unitary limit has to be assumed to achi eve agreement with recent theoretical results. Including published infrared results we present sigma(1)(nu) in the spectral range from 0.1-100 THz. [S 0163-1829(99)01605-7].