Shubnikov-de Haas oscillations near the metal-insulator transition in a   two-dimensional electron system in silicon
  We have studied Shubnikov-de Haas oscillations in a two-dimensional electron system in silicon at low electron densities. Near the metal-insulator transition, only "spin" minima of the resistance at Landau-level filling factors 2, 6, 10, and 14 are seen, while the "cyclotron" minima at filling factors 4, 8, and 12 disappear. A simple explanation of the observed behavior requires a giant enhancement of the spin splitting near the metal-insulator transition. 
S. V. Kravchenko, A. A. Shashkin, David A. Bloore, and T. M. Klapwijk