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 v = 2, 6, 10, and 14 are seen, while the 'cyclotron' minima at v = 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. (C) 2000 Elsevier Science Ltd. All rights reserved.