Coherence measurements of polaritons in thermal equilibrium reveal a power law for two-dimensional condensates

TL;DR

This study experimentally and numerically investigates the coherence properties of a two-dimensional polariton condensate in thermal equilibrium, revealing a novel power law relationship between coherent fraction and density.

Contribution

It demonstrates the existence of a power law for coherence in 2D polariton condensates, supported by both experiments and simulations, which was not predicted by previous theories.

Findings

Power law relation between coherent fraction and density observed

Coherent fraction measured across a wide density range

Numerical simulations confirm experimental results

Abstract

We have created a spatially homogeneous polariton condensate in thermal equilibrium, up to very high condensate fraction. Under these conditions, we have measured the coherence as a function of momentum, and determined the total coherent fraction of this boson system from very low density up to density well above the condensation transition. These measurements reveal a consistent power law for the coherent fraction as a function of the total density over nearly three orders of its magnitude. The same power law is seen in numerical simulations solving the two-dimensional Gross-Pitaevskii equation for the equilibrium coherence. This power law has not been predicted by prior analytical theories.