Interaction-induced topological properties of two bosons in flat-band systems

TL;DR

This paper explores how interactions between two bosons in flat-band systems can induce topological states, revealing tunable topological properties and flat-band localization phenomena through theoretical modeling and numerical analysis.

Contribution

It demonstrates the emergence of interaction-induced topological states in flat-band bosonic systems and provides effective models and numerical evidence for their robustness.

Findings

Interaction-induced topological states can be tuned in flat-band systems.

Topological states persist for strong interactions and away from flat-band conditions.

Doubly localized flat-band states lead to Aharonov-Bohm cage phenomena.

Abstract

In flat-band systems, destructive interference leads to the localization of non-interacting particles and forbids their motion through the lattice. However, in the presence of interactions the overlap between neighbouring single-particle localized eigenstates may enable the propagation of bound pairs of particles. In this work, we show how these interaction-induced hoppings can be tuned to obtain a variety of two-body topological states. In particular, we consider two interacting bosons loaded into the orbital angular momentum $l=1$ states of a diamond-chain lattice, wherein an effective $\pi$ flux may yield a completely flat single-particle energy landscape. In the weakly-interacting limit, we derive effective single-particle models for the two-boson quasiparticles which provide an intuitive picture of how the topological states arise. By means of exact diagonalization calculations, we benchmark these states and we show that they are also present for strong interactions and away from the strict flat-band limit. Furthermore, we identify a set of doubly localized two-boson flat-band states that give rise to a special instance of Aharonov-Bohm cages for arbitrary interactions.