THE STAGGERED CHARGE-ORDER PHASE OF THE EXTENDED HUBBARD MODEL

TL;DR

This paper analyzes the phase diagram of the extended Hubbard model at low temperatures, revealing the merging of staggered phases into a single region without phase transitions, using Pirogov-Sinai theory.

Contribution

It provides a detailed low-temperature analysis of the extended Hubbard model's phase diagram, identifying the merging of staggered phases into one region.

Findings

Three staggered regions merge into one at low temperature

No phase transitions occur within the merged staggered region

The phase diagram is characterized by analytic free energy and order parameters

Abstract

We study the phase diagram of the extended Hubbard model in the atomic limit. At zero temperature, the phase diagram decomposes into six regions: three with homogeneous phases (characterized by particle densities $\rho=0$, 1, and 2 and staggered charge density $\Delta=0$) and three with staggered phases (characterized by the densities $\rho=\frac12$, 1, and $\frac32$ and staggered densities $|\Delta|=\frac12$, 1, and $\frac12$). Here we use Pirogov-Sinai theory to analyze the details of the phase diagram of this model at low temperatures. In particular, we show that for any sufficiently low nonzero temperature the three staggered regions merge into one staggered region $S$, without any phase transitions (analytic free energy and staggered order parameter $\Delta$) within $S$.