Optical study of superconductingPr2CuOxwithx≃4

Abstract

Superconducting ${\mathrm{Pr}}_{2}$${\mathrm{CuO}}_{x},x\ensuremath{\simeq}4$ (PCO), films with ${T}^{\ensuremath{'}}$ structure and a ${T}_{c}$ of 27 K have been investigated by various optical methods in a wide frequency $(7--55 000{\mathrm{cm}}^{\ensuremath{-}1})$ 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 $300{\mathrm{cm}}^{\ensuremath{-}1}$ 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 $1.6\ensuremath{\mu}\text{m}$, indicating a rather low density of the superconducting condensate.