Equilibrium Phases of Tilted Dipolar Lattice Bosons

TL;DR

This study maps the phase diagram of tilted dipolar bosons in a 2D optical lattice, revealing superfluid, checkerboard, stripe solid, and micro-emulsion phases, with implications for experimental realization.

Contribution

It provides the first detailed analysis of zero- and finite-temperature phases of tilted dipolar bosons, including the discovery of a micro-emulsion phase and phase transition characteristics.

Findings

Superfluid phase exists below a critical interaction strength for all tilt angles.

Checkerboard and stripe solid phases emerge at higher interactions depending on tilt.

Stripe solid phase is most stable against thermal fluctuations.

Abstract

The recent advances in creating nearly degenerate quantum dipolar gases in optical lattices are opening the doors for the exploration of equilibrium physics of quantum systems with anisotropic and long-range dipolar interactions. In this paper we study the zero- and finite-temperature phase diagrams of a system of hard-core dipolar bosons at half-filling, trapped in a two-dimensional optical lattice. The dipoles are aligned parallel to one another and tilted out of the optical lattice plane by means of an external electric field. At zero-temperature, the system is a superfluid at all tilt angles $\theta$ provided that the strength of dipolar interaction is below a critical value $V_c(\theta)$. Upon increasing the interaction strength while keeping $\theta$ fixed, the superfluid phase is destabilized in favor of a checkerboard or a stripe solid depending on the tilt angle. We explore the nature of the phase transition between the two solid phases and find evidence of a micro-emulsion phase, following the Spivak-Kivelson scenario, separating these two solid phases. Additionally, we study the stability of these quantum phases against thermal fluctuations and find that the stripe solid is the most robust, making it the best candidate for experimental observation.