Anomalous Behavior of Spin Systems with Dipolar Interactions

TL;DR

This paper investigates two-dimensional spin systems with dipolar interactions, revealing unique long-range order and anomalous ground state correlations due to the long-distance tail of dipole-dipole interactions.

Contribution

It introduces a spin wave theory that fully accounts for dipolar tails, uncovering novel features absent in short-range interaction models.

Findings

Existence of true long-range order at finite temperature in 2D dipolar systems.

Anomalous ground state correlations not seen in short-range models.

Distinct spin wave excitation spectrum due to dipolar interactions.

Abstract

We study the properties of spin systems realized by cold polar molecules interacting via dipole-dipole interactions in two dimensions. Using a spin wave theory, that allows for the full treatment of the characteristic long-distance tail of the dipolar interaction, we find several anomalous features in the ground state correlations and the spin wave excitation spectrum, which are absent in their counterparts with short range interaction. The most striking consequence is the existence of true long-range order at finite temperature for a two-dimensional phase with a broken U(1) symmetry.