ABOUT LONG RANGE PAIRING CORRELATIONS IN THE HUBBARD AND U-t-t’ MODELS

Abstract

Using a quantum Monte Carlo method we measured pair correlation functions with different symmetries as a function of the filling, U/t and t'/t for the Hubbard and U-t-t' models. For the first time we present Monte Carlo results for U/t larger than the bandwidth 8t, away from half-filling. D-wave and extended S-wave pairing correlations are enhanced. D-wave pairing is stronger at half-filling but this behavior is reversed when the filling decreases. However, none of the eight pairing correlations that we studied increases as a function of lattice size, which makes the existence of long range superconducting order unlikely.