Two-dimensional supersolidity in a planar dipolar Bose gas

TL;DR

This paper explores the phase diagram and superfluid properties of a two-dimensional dipolar Bose-Einstein condensate, identifying conditions for supersolidity and analyzing different crystalline phases.

Contribution

It provides a detailed phase diagram of 2D dipolar BECs, introduces simplified theories for ground states, and links supersolidity to roton softening phenomena.

Findings

Triangular, honeycomb, and stripe phases identified

Stripe phase shows anisotropic superfluidity

Phase diagram extended to low density regime

Abstract

We investigate the crystalline stationary states of a dipolar Bose-Einstein condensate in a planar trapping geometry. Our focus is on the ground state phase diagram in the thermodynamic limit, where triangular, honeycomb and stripe phases occur. We quantify the superfluid fraction by calculating the non-classical translational inertia, which allows us to identify favorable parameter regimes for observing supersolid ground states. We develop two simplified theories to approximately describe the ground states, and consider the relationship to roton softening in the uniform ground state. This also allows us to extend the phase diagram to the low density regime. While the triangular and honeycomb states have an isotropic superfluid response tensor, the stripe state exhibits anisotropic superfluidity.