Devil's staircases and supersolids in a one-dimensional dipolar Bose gas

TL;DR

This paper explores the complex phase diagram of a one-dimensional dipolar Bose gas, revealing a devil's staircase of stable states, and introduces supersolid phases emerging from the interplay of interactions and hopping.

Contribution

It provides a detailed analysis of the phase diagram, including the effects of hopping and onsite interaction reduction, and predicts the emergence of supersolid phases in a dipolar Bose gas.

Findings

Complete devil's staircase of stable states at zero hopping and strong interactions.

Hopping introduces competition between Mott insulators and superfluid phases.

Softening onsite interactions leads to supersolids with simultaneous order and superfluidity.

Abstract

We consider a single-component gas of dipolar bosons confined in a one-dimensional optical lattice, where the dipoles are aligned such that the long-ranged dipolar interactions are maximally repulsive. In the limit of zero inter-site hopping and sufficiently large on-site interaction, the phase diagram is a complete devil's staircase for filling fractions between 0 and 1, wherein every commensurate state at a rational filling is stable over a finite interval in chemical potential. We perturb away from this limit in two experimentally motivated directions involving the addition of hopping and a reduction of the onsite interaction. The addition of hopping alone yields a phase diagram, which we compute in perturbation theory in the hopping, where the commensurate Mott phases now compete with the superfluid. Further softening of the onsite interaction yields alternative commensurate states with double occupancies which can form a staircase of their own, as well as one-dimensional "supersolids" which simultaneously exhibit discrete broken symmetries and superfluidity.