Anomalous robustness of the 5/2 fractional quantum Hall state near a sharp phase boundary

TL;DR

This study reveals an unexpected robustness of the 5/2 fractional quantum Hall state near a phase boundary in GaAs quantum wells, with a sudden transition indicating a possible first-order phase change.

Contribution

It demonstrates the anomalous stability of the 5/2 state near a Landau level crossing in wide GaAs quantum wells, highlighting a sharp phase transition.

Findings

5/2 state remains stable and even strengthens near the LL crossing

Sudden disappearance of the 5/2 state suggests a first-order transition

Transition from quantum Hall state to metallic state as Fermi energy shifts

Abstract

We report magneto-transport measurements in wide GaAs quantum wells with tunable density to probe the stability of the fractional quantum Hall effect at filling factor $\nu = $ 5/2 in the vicinity of the crossing between Landau levels (LLs) belonging to the different (symmetric and antisymmetric) electric subbands. When the Fermi energy ($E_F$) lies in the excited-state LL of the symmetric subband, the 5/2 quantum Hall state is surprisingly stable and gets even stronger near this crossing, and then suddenly disappears and turns into a metallic state once $E_F$ moves to the ground-state LL of the antisymmetric subband. The sharpness of this disappearance suggests a first-order transition.