Ferromagnetic Fractional Quantum Hall States in a Valley-Degenerate Two-Dimensional Electron System

TL;DR

This study investigates quantum Hall states in a two-valley 2D electron system, revealing persistent states at certain filling factors and highlighting discrepancies between observed energy gaps and existing theories for anisotropic valleys.

Contribution

It provides the first experimental exploration of ferromagnetic fractional quantum Hall states in a valley-degenerate, anisotropic 2D electron system, comparing measurements to theoretical predictions.

Findings

Quantum Hall states persist at zero strain with valley degeneracy.

Measured energy gaps are smaller than theoretical predictions for single-valley systems.

Gaps and their strain dependence differ significantly from existing models.

Abstract

We study a two-dimensional electron system where the electrons occupy two conduction band valleys with anisotropic Fermi contours and strain-tunable occupation. We observe persistent quantum Hall states at filling factors $\nu = 1/3$ and 5/3 even at zero strain when the two valleys are degenerate. This is reminiscent of the quantum Hall ferromagnet formed at $\nu = 1$ in the same system at zero strain. In the absence of a theory for a system with anisotropic valleys, we compare the energy gaps measured at $\nu = 1/3$ and 5/3 to the available theory developed for single-valley, two-spin systems, and find that the gaps and their rates of rise with strain are much smaller than predicted.