THE FRICTIONAL DRAG BETWEEN COUPLED 2-DIMENSIONAL ELECTRONIC SYSTEMS IN MAGNETIC-FIELDS

The coupling between systems of two spatially separated two-dimensiona l (2D) electron gases and between systems of a separated 2D electron g as and a 2D hole gas is studied as a function of magnetic field B. The coupled electron gases with a barrier of 30 nm showed a transition fr om a phonon-dominated interaction at B = 0 to a Coulomb dominated one at quantising fields. For larger barriers (190 nm), phonons have been found to be the dominant coupling mechanism both at zero and finite fi elds. However, for all barriers investigated, we could observe a suppr ession of the coupling at half-filled Landau-levels probably due to no vel screening effects. In the case of the coupled electron-hole gas sa mples with large barriers (>190 nm) we have investigated, the enhanced screening effects could not be observed possibly due to the less pron ounced quantisation of the hole gas. (C) 1998 Elsevier Science B.V. Al l rights reserved.