Observation of an anomalous density-dependent energy gap of the $\nu=5/2$ fractional quantum Hall state in the low density regime

TL;DR

This study investigates the $ u=5/2$ fractional quantum Hall state at very low electron densities, revealing an anomalous density-dependent energy gap change potentially linked to a topological phase transition.

Contribution

It reports the first observation of an anomalous density dependence of the energy gap in the $ u=5/2$ state at low densities, suggesting new physics in the fractional quantum Hall regime.

Findings

Anomalously large change in energy gap near $ ho=5.8 imes 10^{10}$~cm$^{-2}$

Possible indication of a topological phase transition

Density dependence of the energy gap deviates from previous expectations

Abstract

We have studied the $\nu=5/2$ fractional quantum Hall state in a density-tunable sample at extremely low electron densities. For the densities accessed in our experiment, the Landau level mixing parameter $\kappa$ spans the $2.52<\kappa<2.82$ range. In the vicinity of $5.8 \times 10^{10}$~cm$^{-2}$ or $\kappa = 2.6$ an anomalously large change in the density dependence of the energy gap is observed. Possible origins of such an anomaly are discussed, including a topological phase transition in the $\nu=5/2$ fractional quantum Hall state.