Evolution of the 7/2 fractional quantum Hall state in two-subband systems

TL;DR

This study investigates how the fractional quantum Hall state at filling factor 7/2 evolves in wide GaAs quantum wells with two occupied subbands, revealing persistent features linked to the 5/2 state under various conditions.

Contribution

It demonstrates the evolution of the 7/2 fractional quantum Hall state in two-subband systems and uncovers the persistence of the 5/2 state under asymmetric charge distributions.

Findings

Persistence of resistance minimum near 7/2 under asymmetric conditions

Level crossing at the Fermi energy correlates with 5/2 filling

Development of 5/2 FQHS in symmetric subband

Abstract

We report the evolution of the fractional quantum Hall state (FQHS) at even-denominator filling factor $\nu=7/2$ in wide GaAs quantum wells in which electrons occupy two electric subbands. The data reveal subtle and distinct evolutions as a function of density, magnetic field tilt-angle, or symmetry of the charge distribution. When the charge distribution is strongly asymmetric, there is a remarkable persistence of a resistance minimum near $\nu=7/2$ when two Landau levels belonging to the two subbands cross at the Fermi energy. The field position of this minimum tracks the 5/2 filling of the symmetric subband, suggesting a pinning of the crossing levels and a developing 5/2 FQHS in the symmetric subband even when the antisymmetric level is partially filled.