Two-dimensional electrical transport in GaAs-AlxGa1−xAsmultilayers at high magnetic fields

We have studied the magnetotransport properties of two-dimensional electrons in thin GaAs-${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ multilayers with fields up to 210 kG from 4.2 to 2.4 K. We observed that ${\rho }_{\mathrm{xx}}$ decreases with decreasing $T$ in the high-field limit $\nu =2\mathrm{}\pi n{l}_0^2\lesssim 1$, but ${\rho }_{\mathrm{xy}}$ shows no such changes. We show that this result cannot be explained by models based on independent electrons and suggest as possible explanations the formation of a highly correlated state, such as a charge-density wave or Wigner solid previously suggested for the Si inversion layer, and the enhancement of $g$ factor at $\nu \lesssim 1$.