Optical study of superconducting Pr2 CuOx with x x≃4

Superconducting Pr2CuOx,x≃4 (PCO), films with T′ structure and a Tc of 27 K have been investigated by various optical methods in a wide frequency (7–55 000cm−1) and temperature (2–300 K) range. The optical spectra do not reveal any indication of a normal-state gap formation. A Drude-like peak centered at zero frequency dominates the optical conductivity below 150 K. At higher temperatures, it shifts to finite frequencies. The detailed analysis of the low-frequency conductivity reveals that the Drude peak and a far-infrared (FIR) peak centered at about 300cm−1 persist at all temperatures. The FIR-peak spectral weight is found to grow at the expense of the Drude spectral weight with increasing temperature. The temperature dependence of the penetration depth follows a behavior typical for d-wave superconductors. The absolute value of the penetration depth for zero temperature is 1.6μm, indicating a rather low density of the superconducting condensate