Electronic c-axis response of Y1-xCaxBa2Cu3O7-δ 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 the normal state, in particular, the "pseudogap." is determined by the CuO2 planes which confine the charge carriers. In the overdoped regime this confinement is relaxed. Simultaneously, the superconducting energy gap is reduced and a large fraction of the quasiparticles remains unpaired below T-c.