ELECTRONIC C-AXIS RESPONSE OF Y1-XCAXBA2CU3O7-DELTA CRYSTALS STUDIED BY FAR-INFRARED ELLIPSOMETRY

We studied the electronic c-axis conductivity sigma(c)(cl)(omega,T) of Y1-xCaxBa2Cu3O7-delta by far-infrared ellipsometry. The substitution of Y3+ bf Ca2+ makes the overdoped regime accessible and decouples the electronic properties of CuO2 planes and CuO chains. We find evidence that the unusual omega and T dependence of sigma(c)(cl)(omega,T) in t he normal state, in particular, the ''pseudogap.'' is determined by th e CuO2 planes which confine the charge carriers. In the overdoped regi me this confinement is relaxed. Simultaneously, the superconducting en ergy gap is reduced and a large fraction of the quasiparticles remains unpaired below T-c.