ONSET OF SUBBAND LOCKING IN DOUBLE-QUANTUM-WELL STRUCTURES AS THE SIGNATURE OF WAVE-FUNCTION DELOCALIZATION

We have studied a series of double-quantum-well structures with differ ent barrier thicknesses by means of magnetoresistivity measurements. W hereas wide-barrier samples show predominantly double-layer behaviour, single-layer behaviour is increasingly observed for narrower barrier systems even when two subbands are occupied. This single-layer behavio ur is caused by charge transfer between the two occupied subbands and the concomitant locking together of their subband energies. We explain this transition as an immediate consequence of the degree of wave fun ction delocalization. Our magnetoresistivity measurements are supporte d by model calculations that confirm this explanation. (C) 1998 Elsevi er Science B.V. All rights reserved.