Emergent Mott-insulators at non-integer fillings and devil's staircase induced by attractive interaction in many-body polarons

TL;DR

This paper explores how attractive interactions among many-body polarons in ultracold atoms lead to novel phases, including self-bound superfluids and non-integer Mott-insulators with devil's staircase structures, observable in current experiments.

Contribution

It reveals the emergence of Mott-insulators at non-integer fillings and a devil's staircase pattern driven by attractive interactions in many-body polaron systems.

Findings

Attractive interactions induce self-bound superfluid phases.

Deep optical lattices support non-integer Mott-insulators.

System exhibits devil's staircase structure in effective density.

Abstract

We investigate the ground state properties of an ultracold atom system consisting of many-body polarons, quasiparticles formed by impurity atoms in optical lattices immersing in a Bose-Einstein condensate. We find the nearest-neighbor attractive interaction between polarons can give rise to rich physics that is peculiar to this system. In a relatively shallow optical lattice, the attractive interaction can drive the system being in a self-bound superfluid phase with its particle density distribution manifesting a self-concentrated structure. While in a relatively deep optical lattice, the attractive interaction can drive the system forming the Mott-insulator phase even though the global filling factor is not integer. Interestingly, in the Mott-insulator regime, the system can support a series of different Mott-insulators with their effective density manifesting a devil's staircase structure with respect to the strength of attractive interaction. Detailed estimation on relevant experimental parameters shows that these rich physics can be readily observed in current experimental setups.