A two-fluid model for the normal-state properties of cuprate superconductors

We consider a two-dimensional metal with metallic layers of width d separated by thick layers with a large dielectric constant e{open}₂. Electronic states near the Fermi surface are renormalized so that their velocity increases significantly, as in the Lindhard model. In contrast, states removed from the FS are renormalized so that their velocity decreases, as described by the Gutzwiller theory. We suggest that these two types of states are decoupled, and can be described by a two-fluid model. The resistivity of the FS fluid, due to elastic scattering, becomes temperature-dependent, decreasing significantly at T=0 and actually vanishing as we approach the Mott transition. The increased velocity accounts for the small London penetration depth found in the superconducting state. This model can also account for the zero bias anomaly observed in some "exotic" superconductors.