Observation of a transition from a topologically ordered to a spontaneously broken symmetry phase

TL;DR

This paper reports a rare transition in a 2D electron gas where a topologically ordered fractional quantum Hall state spontaneously transitions to a nematic phase with broken symmetry, driven by hydrostatic pressure.

Contribution

It demonstrates a spontaneous transition from a topologically ordered phase to a symmetry-broken phase in a quantum Hall system, bridging two distinct classes of matter phases.

Findings

Observation of a spontaneous topological to symmetry-broken phase transition

Identification of a quantum Hall nematic phase emerging without external fields

Pressure-induced transition in a fractional quantum Hall state

Abstract

Until the late 1980s, phases of matter were understood in terms of Landau's symmetry breaking theory. Following the discovery of the quantum Hall effect the introduction of a second class of phases, those with topological order, was necessary. Phase transitions within the first class of phases involve a change in symmetry, whereas those between topological phases require a change in topological order. However, in rare cases transitions may occur between the two classes in which the vanishing of the topological order is accompanied by the emergence of a broken symmetry. Here, we report the existence of such a transition in a two-dimensional electron gas hosted by a GaAs/AlGaAs crystal. When tuned by hydrostatic pressure, the $\nu=5/2$ fractional quantum Hall state, believed to be a prototype non-Abelian topological phase, gives way to a quantum Hall nematic phase. Remarkably, this nematic phase develops spontaneously, in the absence of any externally applied symmetry breaking fields.