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

Magnetotransport measurements in a two-layer electron system with larg e spacing between the layers are reported. The application of differen tial methods allows us to investigate each of the two conducting layer s separately. At low magnetic fields we observe additional high-mobili ty carriers located between the two conducting layers forming an exten ded electronic state. With increasing magnetic field these electrons a re frozen out. The spin-split integer quantum Hall states and the frac tional 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 diff erential magnetotransport studies.