Frustration induced incommensurate solids in the extended Bose-Hubbard model

TL;DR

This paper investigates how frustration from weak next-nearest-neighbor interactions in the extended Bose-Hubbard model leads to the stabilization of incommensurate solid phases with fractional densities, revealing a domain wall formation mechanism.

Contribution

It demonstrates the emergence of incommensurate solids in the extended Bose-Hubbard model with weak frustration, expanding understanding of phase stability in such quantum lattice systems.

Findings

Incommensurate solids with fractional densities from 1/4 to 1/2 are stabilized.

Wave vectors of these solids vary continuously from $(\pi,rac{\pi}{2})$ to $(\pi,\pi)$.

Domain wall formation explains the incommensurate phase mechanism.

Abstract

We study the extended Bose-Hubbard model with nearest-neighbor and next-nearest-neighbor $(V, V')$ repulsive interactions on a square lattice by using the quantum Monte Carlo method. Unlike the case of strong $V'$ where the ground states can be striped solids or striped supersolids, we focus on weak $V' < V/2$ and small hoppings and find that, in the thermodynamic limit, incommensurate solids of fractional densities varying from 1/4 to 1/2 can be stabilized. We also show that the incommensurate solids, which are characterized by a continuous set of wave vectors changing from $(\pi,\pi/2)$ (or $(\pi/2,\pi)$) to $(\pi,\pi)$, can be understood by a mechanism of domain wall formation. The related ground-state phase diagram and thermal phase transitions are also discussed.