Bilayer crystals in a polar-molecules system

TL;DR

This study uses Quantum Monte Carlo simulations to map the finite-temperature phase diagram of polar molecules in a quasi-2D setup, revealing various phases including bilayer crystals and superfluid states influenced by temperature and confinement.

Contribution

It provides the first detailed phase diagram of polar molecules in a quasi-2D geometry, highlighting the stabilization of bilayer crystals and layered superfluidity through confinement tuning.

Findings

Crystallization occurs with increasing temperature due to thermal fluctuations.

A bilayer crystal with one molecule per site can be stabilized by confinement.

Layered superfluid states with phase coherence between layers are observed.

Abstract

We investigate the finite-temperature phase diagram of polar molecules confined in a quasi-two-dimensional geometry by a harmonic potential along the polarization axis. We employ Quantum Monte Carlo simulations to explore the strongly correlated regime accessible with current experimental setups. By tuning temperature and confinement strength, we identify a rich set of phases, including normal fluid, superfluid, supersolid, cluster crystal, and bilayer crystal states. Our results reveal the emergence of crystallization upon increasing temperature, highlighting the nontrivial role of thermal fluctuations in dipolar systems. In particular, we show that a bilayer crystal with one molecule per lattice site can be stabilized by varying the confinement strength at fixed interaction. Moreover, we show evidence of layering of superfluid states with phase coherence between the two layers. These findings provide insight into the interplay between interactions, confinement, and temperature in low-dimensional dipolar systems, and suggest new directions for engineering quantum phases with ultracold polar molecules.