Bond-charge Interaction in the extended Hubbard chain

TL;DR

This study investigates how bond-charge interactions influence the phases and correlations in the extended 1D Hubbard model, revealing enhanced charge-density-wave robustness, intermediate phases, and unusual spin correlations, with no pairing enhancement observed.

Contribution

It provides new insights into the effects of bond-charge interactions on phase stability and correlation functions in the extended Hubbard model at half-filling.

Findings

Charge-density-wave state is more robust than spin-density-wave state regardless of X.

Small bond-charge interactions reduce differences between CDW and SDW correlations.

An intermediate phase with multiple critical points appears for X=t and V<2t.

Abstract

We study the effects of bond-charge interaction (or correlated hopping) on the properties of the extended ({\it i.e.,} with both on-site ($U$) and nearest-neighbor ($V$) repulsions) Hubbard model in one dimension at half-filling. Energy gaps and correlation functions are calculated by Lanczos diagonalization on finite systems. We find that, irrespective of the sign of the bond-charge interaction, $X$, the charge--density-wave (CDW) state is more robust than the spin--density-wave (SDW) state. A small bond-charge interaction term is enough to make the differences between the CDW and SDW correlation functions much less dramatic than when $X=0$. For $X=t$ and fixed $V<2t$ ($t$ is the uncorrelated hopping integral), there is an intermediate phase between a charge ordered phase and a phase corresponding to singly-occupied sites, the nature of which we clarify: it is characterized by a succession of critical points, each of which corresponding to a different density of doubly-occupied sites. We also find an unusual slowly decaying staggered spin-density correlation function, which is suggestive of some degree of ordering. No enhancement of pairing correlations was found for any $X$ in the range examined.