Ringlike structures in the density--magnetic-field $\rho_{xx}$ diagram   of two-subband quantum Hall systems
  Motivated by recent experiments [Zhang \textit{et al.}, Phys. Rev. Lett. \textbf{95}, 216801 (2005) and Ellenberger \textit{et al.}, cond-mat/0602271] reporting novel ringlike structures in the density--magnetic-field ($n_{2D}$\emph{--B}) diagrams of the longitudinal resistivity $\rho_{xx}$ of quantum wells with two subbands, we investigate theoretically here the magneto-transport properties of these quantum-Hall systems. We determine $\rho_{xx}$ via both the Hartree and the Kohn-Sham self-consistent schemes plus the Kubo formula. While the Hartree calculation yields diamond-shaped structures in the $n_{2D}$\emph{--B} diagram, the calculation including exchange and correlation effects (Kohn-Sham) more closely reproduces the ringlike structures in the experiments. 
Gerson J. Ferreira, Henrique J. P. Freire, J. Carlos Egues