Multiple Phases with the Same Quantized Hall Conductance in a Two-Subband System

TL;DR

This paper investigates complex topological features in a two-subband GaAs/AlGaAs system, revealing ring-like structures in the phase diagram linked to ferromagnetic quantum Hall states caused by electron interactions.

Contribution

It demonstrates that the observed ring structures are due to ferromagnetic quantum Hall states arising from interactions between energy levels with opposite spins and different subbands.

Findings

Ring-like structures observed at even integer filling factors.

Activation energies within rings are significantly smaller.

Simple single particle models cannot explain these features.

Abstract

In a GaAs/AlGaAs two-dimensional electron system with two occupied subbands, the experimentally determined phase diagram in the density-magnetic field plane exhibits rich topological features. Ring-like structures are observed at even integer filling factors, in the phase diagram. Even with the identical quantized Hall resistance values as those given rise by the ordinary integer quantum Hall effect due to the Landau level quantization; the activation energies of these states within the rings are much smaller. These ring structures cannot account for by the simple single particle picture. We argue that ferromagnetic quantum Hall states, due to the interaction of two energy levels with opposite spin and different subband indices, are responsible for these unusual structures.