Possible Exotic Phases in the One-Dimensional Extended Hubbard Model

TL;DR

This study uses advanced quantum Monte Carlo simulations to map the phase diagram of the one-dimensional extended Hubbard model, revealing earlier-than-expected phase separation and complex fluctuation behaviors, especially near half filling.

Contribution

It provides the first large-scale numerical analysis clarifying the phase separation boundary and fluctuation characteristics in the model, especially in the V >> U regime.

Findings

Phase separation occurs at smaller V than previously thought.

Superconducting fluctuations are not dominant in the V < V_PS region.

Charge-density fluctuations are strong and gapped, not typical of standard Luttinger Liquids.

Abstract

We investigate numerically the ground state phase diagram of the one-dimensional extended Hubbard model, including an on--site interaction U and a nearest--neighbor interaction V. We focus on the ground state phases of the model in the V >> U region, where previous studies have suggested the possibility of dominant superconducting pairing fluctuations before the system phase separates at a critical value V=V_PS. Using quantum Monte Carlo methods on lattices much larger than in previous Lanczos diagonalization studies, we determine the boundary of phase separation, the Luttinger Liquid correlation exponent K_rho, and other correlation functions in this region. We find that phase separation occurs for V significantly smaller than previously reported. In addition, for negative U, we find that a uniform state re-enters from phase separation as the electron density is increased towards half filling. For V < V_PS, our results show that superconducting fluctuations are not dominant. The system behaves asymptotically as a Luttinger Liquid with K_rho < 1, but we also find strong low-energy (but gapped) charge-density fluctuations at a momentum not expected for a standard Luttinger Liquid.