Constructing quasiparticle operators in strongly correlated systems

In models of strongly correlated electrons the wave-function renormalization ${\mathit{Z}}_{\mathit{h}}$ of a hole injected in a half-filled band is small compared to unity. This result reduces the accuracy of numerical and analytical predictions of superconductivity for the Hubbard and related models. A simple method is described to deduce approximate quasiparticle operators whose ${\mathit{Z}}_{\mathit{h}}$ is closer to 1 than for the standard bare operators. The method is tested for the t-J model. We find that pairing operators constructed out of these quasiparticles are also considerably improved. For example, at J/t=0.2 an improvement by a factor of 10 or more is expected in the signal of superconductivity in a Monte Carlo simulation if these quasiparticle operators are used rather than the standard bare operators.