Spin-Polarization of Composite Fermions and Particle-Hole Symmetry Breaking

TL;DR

This study investigates how the critical spin-polarization energy in fractional quantum Hall states varies with quantum well width and suggests particle-hole symmetry breaking, supported by experimental data and theoretical modeling.

Contribution

It provides experimental evidence of particle-hole symmetry breaking in fractional quantum Hall states and compares it with theoretical models including Landau level mixing.

Findings

$oldsymbol{ ext{Critical spin-polarization energy decreases with increasing well width}}$

$oldsymbol{ ext{Asymmetry in $ u=3/2$ and $ u=1/2$ states indicates particle-hole symmetry breaking}}$

$oldsymbol{ ext{Theoretical models qualitatively reproduce experimental trends}}$

Abstract

We study the critical spin-polarization energy ($\alpha_{\rm C}$) above which fractional quantum Hall states in two-dimensional electron systems confined to symmetric GaAs quantum wells become fully spin-polarized. We find a significant decrease of $\alpha_{\rm C}$ as we increase the well-width. In systems with comparable electron layer thickness, $\alpha_{\rm C}$ for fractional states near Landau level filling $\nu=3/2$ is about twice larger than those near $\nu=1/2$, suggesting a broken particle-hole symmetry. Theoretical calculations, which incorporate Landau level mixing through an effective three-body interaction, and finite layer thickness, capture certain qualitative features of the experimental results.