Interacting Bose gases in twisted-bilayer optical lattices

TL;DR

This paper explores the complex ground-state phases of interacting bosons in twisted-bilayer optical lattices, revealing novel Mott-like and Bose glass phases influenced by clusterization and twist angle commensurability.

Contribution

It introduces a tailored cluster Gutzwiller approach to accurately capture the effects of site clusterization in twisted-bilayer lattices, uncovering new phases and mobility phenomena.

Findings

Identification of diverse Mott-like phases with different cluster occupations.

Discovery of pockets of freely moving but disconnected sites resembling Bose glass.

Mobility islands can form purely from inter-layer interactions without hopping.

Abstract

Recent experiments have realized ultra-cold gases in twisted-bilayer optical lattices. We show that interacting bosons in these lattices present a highly non-trivial ground-state physics resulting from the interplay between inter- and intra-layer hopping and interactions. This physics is crucially determined by site clusterization, which we properly take into account by developing a specifically-tailored cluster Gutzwiller approach. Clusterization results in a large variety of different Mott-like phases characterized by typically different occupations of the clusters, and in the appearance of pockets of sites in between which particles can freely move, but which remain disconnected from each other. This peculiar phase, which resembles the well-known Bose glass phase, may occur even for commensurate twist angles and is further enhanced when the twisting is incommensurate. Moreover, in the incommensurate case, the formation of mobility islands may occur even without inter-layer hopping solely due to inter-layer interactions.