Spin-Polarization of Composite Fermions and Particle-Hole Symmetry   Breaking
  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. 
Yang Liu, S. Hasdemir, A. W\'ojs, J.K. Jain, L.N. Pfeiffer, K.W. West,   K.W. Baldwin, M. Shayegan
cond-mat.mes-hall cond-mat.str-el