OPTICAL-PROPERTIES OF OVERDOPED YBA2CU3OX-PARALLEL-TO-C - EVIDENCE FOR SUPERCONDUCTIVITY IN THE CHAINS

We report on temperature-dependent reflectance measurements on several YBa2Cu3Ox single crystals with 6.8 less than or equal to x less than or equal to 7 in the far-infrared range (5 meV < (h) over bar omega < 100 meV) with E parallel to c. Performing a Kramers-Kronig transformat ion, we derive the optical conductivity sigma(parallel to c)((h) over bar omega) and the real part of the dielectric constant epsilon(1 para llel to c)((h) over bar omega). Fitting the data with a two-fluid mode l, we obtained the superfluid carrier density and the scattering rate. The crystals of oxygen content x < 6.93, i. e. below the maximum valu e of T-c, show a linear dependence of the superfluid carrier density w ith temperature, consistent with the d-wave model. The data for the ov erdoped crystals give evidence for superconductivity of the chain carr iers.