Depolarization shift of the superradiant phase transition

TL;DR

This paper explores how short-range depolarizing interactions affect the superradiant phase transition in atomic gases, finding that these interactions shift the critical density and lead to a condensed phase instead of superradiance.

Contribution

It introduces an extended model including depolarizing interactions and shows their impact on the superradiant phase transition in atomic gases.

Findings

Critical density exists but is increased by depolarizing interactions

System transitions to a condensed phase at critical density

Depolarizing interactions modify the nature of the phase transition

Abstract

We investigate the possibility of a Dicke-type superradiant phase transition of an atomic gas with an extended model which takes into account the short-range depolarizing interactions between atoms approaching each other as close as the atomic size scale, which interaction appears in a regularized electric-dipole picture of the QED of atoms. By using a mean field model, we find that a critical density does indeed exist, though the atom-atom contact interaction shifts it to a higher value than it can be obtained from the bare Dicke-model. We argue that the system, at the critical density, transitions to the condensed rather than the "superradiant" phase.