SUPERFLUID AND NORMAL FLUID DENSITY IN HIGH-T-C SUPERCONDUCTORS

The electronic properties of the cuprate superconductors have been stu died by measuring the reflectance over the frequency range from the fa r-infrared to the near-ultraviolet (roughly, 10 meV-5 eV). There is an interesting behavior in both the normal state and the superconducting state. In the normal state, there is the well-known non-Drude distrib ution of the doping-induced spectral weight. In the superconducting st ate, the spectral weight of the superconducting condensate correlates with T-c in a variety of materials. Remarkably, in optimally doped sup erconductors, only about 20% of the doping-induced carriers joins the superfluid; the rest of the spectral weight remains at finite frequenc ies. (C) 1998 Elsevier Science B.V. All rights reserved.