Superfluidity of Bosons in Kagome Lattices with Frustration

TL;DR

This paper investigates superfluid phases of spinless bosons in a Kagome lattice with a pi flux, revealing a transition from single-boson to exotic triple-boson superfluidity and proposing experimental detection methods.

Contribution

It demonstrates the emergence of a trion superfluid phase in a frustrated Kagome lattice with flat bands, a novel state driven by interactions and frustration.

Findings

Interaction selects a Bloch state at the K point for boson condensation.

A broad temperature regime supports a stable triple-boson superfluid phase.

Time of flight measurements can distinguish between different superfluid phases.

Abstract

In this letter we consider spinless bosons in a Kagome lattice with nearest-neighbor hopping and on-site interaction, and the sign of hopping is inverted by insetting a {\pi} flux in each triangle of Kagome lattice so that the lowest single particle band is perfectly flat. We show that in the high density limit, despite of the infinite degeneracy of the single particle ground states, interaction will select out the Bloch state at the K point of Brillouin zone for boson condensation at the lowest temperature. As temperature increases, the single boson superfluid order can be easily destroyed, while an exotic triple-boson paired superfluid order will remain. We establish that this trion superfluid exists in a broad temperature regime until the temperature is increased to the same order of hopping and then the system turns into normal phases. Finally we show that time of flight measurement of momentum distribution and its noise correlation can be used to distinguish these three phases.