MAGNETOTRANSPORT IN 2 PARALLEL 2-DIMENSIONAL ELECTRON GASES FORMED BY A DELTA-DOPED LAYER AND A HETEROJUNCTION IN GAAS

Magnetotransport measurements in a two-layer electron system with large spacing between the layers are reported. The application of differential methods allows us to investigate each of the two conducting layers separately. At low magnetic fields we observe additional high-mobility carriers located between the two conducting layers forming an extended electronic state. With increasing magnetic field these electrons are frozen out. The spin-split integer quantum Hall states and the fractional quantum Hall states with the filling factors 1/3 and 2/3 of the high-mobility electron gas are found in this two-layer system by differential magnetotransport studies.