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 ν=2, 6, 10, and 14 are seen, while the ‘cyclotron’ minima at ν=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.