Possible realization of the Exciton Bose Liquid phase in a hard-core boson model with ring-only exchange interactions

TL;DR

This paper explores a hard-core boson model with ring exchanges on a square lattice, demonstrating the potential realization of the elusive Exciton Bose Liquid phase through variational wave functions and Quantum Monte Carlo simulations.

Contribution

It introduces a new model with ring-only exchanges and provides evidence for the EBL phase using unbiased quantum Monte Carlo methods.

Findings

EBL phase identified at half-filling for large $K_2$

CDW and valence bond solid phases observed at small and intermediate $K_2$

EBL remains stable at certain densities away from half-filling

Abstract

We investigate a hard-core boson model with ring-only exchanges on a square lattice, where a $K_1$ term acts on 1$\times$1 plaquettes and a $K_2$ term acts on 1$\times$2 and 2$\times$1 plaquettes, with a goal of realizing a novel Exciton Bose Liquid (EBL) phase first proposed by Paramekanti, et al [Phys. Rev. B {\bf 66}, 054526 (2002)]. We construct Jastrow-type variational wave functions for the EBL, study their formal properties, and then use them as seeds for a projective Quantum Monte Carlo study. Using Green's Function Monte Carlo, we obtain an unbiased phase diagram which at half-filling reveals CDW for small $K_2$, valence bond solid for intermediate $K_2$, and possibly for large $K_2$ the EBL phase. Away from half-filling, the EBL phase is present for intermediate $K_2$ and remains stable for a range of densities below 1/2 before phase separation occurs at lower densities.