Evaluation of the two-particle propagator for Hubbard model with the help of Hubbard-I approximation
Abstract
The Hubbard-I approximation is generalized to allow for direct evaluation of the equal-time anomalous two-electron propagator for Hubbard model on two-dimensional square lattice. This propagator is compared against the quantum Monte Carlo data obtained by Aimi and Imada [J. Phys. Soc. Jpn. 76, 113708 (2007)] in the limit of strong electron-electron interaction. The Hubbard-I predictions are in a good qualitative agreement with the Monte Carlo results. In particular, d-wave correlations decay as c r-3 ("free electron" behaviour), if separation r exceeds 2-3 lattice constants. However, the Hubbard-I approximation underestimates coefficient c by a factor of about three. We conclude that the Hubbard-I approximation, despite its simplicity and artefacts, captures the qualitative behaviour of the two-particle propagator for the Hubbard model, at least for moderate values of r.
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