Infrared conductivity in the normal state of cuprate thin films

This paper summarizes the main features of the infrared conductivity spectra in the 500–7000 cm^–1 range derived from room-temperature reflectivity measurements performed on a variety of thin films (YBa₂Cu₃O₇, BiSrCaCuO). The conductivity of these samples decreases with frequency as a power law with an exponent 0.7, and the scattering rate increases linearly with frequency. A detailed comparison with the conductivity for the marginal Fermi liquid (Abrahams, Littlewood, and Varma) and for the Luttinger liquid (Anderson) is performed. In the former case, the effect of temperature appears crucial even in this energy range (T) and allows one to achieve satisfactory fits. In the latter case, both the conductivity and the scattering rate may be accounted for by a single parameter.