Effect of the Three-Site Hopping Term on the t-J Model

TL;DR

This study investigates how the three-site hopping term influences the phase diagram and superconducting correlations in the one-dimensional t-J model using exact diagonalization and quantum Monte Carlo methods.

Contribution

It introduces the effects of the three-site hopping term into the t-J model and analyzes its impact on phase separation and superconducting correlations.

Findings

Suppression of phase separation by the three-site term.

Enhanced local singlet pairing at low electron densities.

Extended spin gap region across various densities.

Abstract

We have used exact diagonalization and quantum Monte Carlo methods to study the one-dimensional {t-J} model including the three-site hopping term derived from the strong coupling limit of the Hubbard model. The three-site term may be important to superconducting correlations since it allows direct hopping of local singlet electron pairs. The phase diagram is determined for several values of the strength of the three-site term and compared with that of the {t-J} and Hubbard models. Phase separation, which exists in the t-J model is suppressed. In the low electron density region the formation of local singlet electron pairs is enhanced, leading to stronger superconducting correlations even for values $J/t<2$. A large spin gap region extends from low electron densities up to high densities. In the low hole density region the superconducting correlations are suppressed at $J/t>2.8$ in spite of enhanced pair formation. This is because the three-site term, while enhancing the formation of electron pairs, leads to a repulsion between holes.