Quantum phase transition in a two-dimensional system of dipoles

TL;DR

This study uses quantum Monte Carlo methods to analyze a 2D dipolar Bose system, revealing a quantum phase transition from gas to solid, with detailed insights into condensate behavior and excitation spectra.

Contribution

It provides the first detailed quantum Monte Carlo analysis of the phase diagram and excitation properties of a 2D dipolar Bose system.

Findings

Identifies a quantum phase transition from gas to solid at specific densities.

Observes a roton minimum in the excitation spectrum near the transition.

Calculates the condensate fraction and static structure factor across phases.

Abstract

The ground-state phase diagram of a two-dimensional Bose system with dipole-dipole interactions is studied by means of quantum Monte Carlo technique. Our calculation predicts a quantum phase transition from gas to solid phase when the density increases. In the gas phase the condensate fraction is calculated as a function of the density. Using Feynman approximation, the collective excitation branch is studied and appearance of a roton minimum is observed. Results of the static structure factor at both sides of the gas-solid phase are also presented. The Lindeman ratio at the transition point comes to be $\gamma = 0.230(6)$. The condensate fraction in the gas phase is estimated as a function of the density.