Spontaneous Symmetry Breaking at the Fluctuating Level

TL;DR

This paper demonstrates that in an isolated diffusive system, large current fluctuations can induce spontaneous symmetry breaking into traveling waves, revealing a new type of phase transition at the fluctuating level.

Contribution

It provides the first experimental observation of symmetry breaking driven by fluctuations in a diffusive system, confirming hydrodynamic fluctuation theory predictions.

Findings

Large fluctuations lead to traveling wave formation.

Gaussian statistics for small fluctuations, non-Gaussian tails for large.

Experimental results agree with hydrodynamic fluctuation theory.

Abstract

Phase transitions not allowed in equilibrium steady states may happen however at the fluctuating level. We observe for the first time this striking and general phenomenon measuring current fluctuations in an isolated diffusive system. While small fluctuations result from the sum of weakly-correlated local events, for currents above a critical threshold the system self-organizes into a coherent traveling wave which facilitates the current deviation by gathering energy in a localized packet, thus breaking translation invariance. This results in Gaussian statistics for small fluctuations but non-Gaussian tails above the critical current. Our observations, which agree with predictions derived from hydrodynamic fluctuation theory, strongly suggest that rare events are generically associated with coherent, self-organized patterns which enhance their probability.