Ultracold bosons in disordered superlattices: Mott-insulators induced by tunneling

TL;DR

This paper investigates how disorder affects the phase diagram of ultracold bosons in a one-dimensional superlattice, revealing disorder-induced Mott-insulating phases and transitions between Bose-glass and Mott insulators.

Contribution

It introduces a detailed analysis of disorder effects on Mott-insulating phases in superlattices using iTEBD and proposes an effective model for understanding these phenomena.

Findings

Disorder destroys loophole-shaped Mott gaps.

Insulating islands emerge at moderate disorder levels.

Transition from Bose-glass to Mott insulator with increasing hopping.

Abstract

We analyse the phase diagram of ultra-cold bosons in a one-dimensional superlattice potential with disorder using the time evolving block decimation algorithm for infinite sized systems (iTEBD). For degenerate potential energies within the unit cell of the superlattice loophole-shaped insulating phases with non-integer filling emerge with a particle-hole gap proportional to the boson hopping. Adding a small amount of disorder destroys this gap. For not too large disorder the loophole Mott regions detach from the axis of vanishing hopping giving rise to insulating islands. Thus the system shows a transition from a compressible Bose-glass to a Mott-insulating phase with increasing hopping amplitude. We present a straight forward effective model for the dynamics within a unit cell which provides a simple explanation for the emergence of Mott-insulating islands. In particular it gives rather accurate predictions for the inner critical point of the Bose-glass to Mott-insulator transition.