Fractional Quantum Hall Effect at High Fillings in a Two-subband Electron System

TL;DR

This study investigates fractional quantum Hall states in a two-subband electron system within a wide GaAs quantum well, revealing new high-filling states and differences from single-subband systems.

Contribution

It demonstrates the distinct fractional quantum Hall sequences at high fillings in a two-subband system and reports new observed states not seen in single-subband systems.

Findings

No even-denominator states at ν=5/2 and 7/2 when Fermi energy is in the ground Landau level.

Observation of states at ν = (i + p/(2p ± 1)) with i=2,3 and p=1,2,3.

Discovery of new fractional states at ν=13/5, 17/5, 18/5, and 25/7.

Abstract

Magneto-transport measurements in a clean two-dimensional electron system confined to a wide GaAs quantum well reveal that, when the electrons occupy two electric subbands, the sequences of fractional quantum Hall states observed at high fillings ($\nu > 2$) are distinctly different from those of a single-subband system. Notably, when the Fermi energy lies in the ground state Landau level of either of the subbands, no quantum Hall states are seen at the even-denominator $\nu$ = 5/2 and 7/2 fillings; instead the observed states are at $\nu = (i + p/(2p \pm 1))$ where $i$ = 2, 3, and $p$ = 1, 2, 3, and include several new states at $\nu$ = 13/5, 17/5, 18/5, and 25/7.