Unusual liquid state of hard-core bosons on the pyrochlore lattice

TL;DR

This paper investigates a novel U(1) fractionalized Mott insulator phase of hard-core bosons on a pyrochlore lattice, characterized by Coulomb phase correlations, which emerges at large repulsion and could be observed in ultracold atom experiments.

Contribution

It identifies and characterizes a U(1) fractionalized Mott insulator phase in a 3D pyrochlore lattice model, linking it to Coulomb phase correlations and experimental signatures.

Findings

Insulating state shows no broken lattice symmetry.

Correlations match Coulomb phase of U(1) gauge theory.

Phase potentially observable in ultracold atom experiments.

Abstract

We study the physics of hard-core bosons with unfrustrated hopping (t) and nearest-neighbor repulsion (V) on the three dimensional pyrochlore lattice. At half-filling, we demonstrate that the small V/t superfluid state eventually becomes unstable at large enough V/t to an unusual insulating state which displays no broken lattice translation symmetry. Equal time and static density correlators in this insulator are well described by a mapping to electric field correlators in the Coulomb phase of a U(1) lattice gauge theory, allowing us to identify this insulator with a U(1) fractionalized Mott-insulating state. The possibility of observing this phase in suitably designed atom-trap experiments with ultracold atoms is also discussed, as are specific experimental signatures.