Projected Wave Functions and High Temperature Superconductivity

We study the Hubbard model with parameters relevant to cuprates using variational Monte Carlo for projected d-wave states. For doping 0<x≲0.35 we obtain a superconductor whose order parameter Φ(x) tracks the observed nonmonotonic T_c(x). The variational parameter Δ_var(x) scales with the (π,0) “hump” and T^* seen in photoemission. Projection leads to incoherence in the spectral function and from the singular behavior of its moments we obtain the nodal quasiparticle weight Z∼x though the Fermi velocity remains finite as x→0. The Drude weight D_low and superfluid density are consistent with experiment and D_low∼Z.