Charge transfer at double-layer to single-layer transition in double-quantum-well systems

Experiments on an abrupt double-layer to single-layer transition in double-quantum-well structures are presented. This transition of an electronic system is observed as a sharp decresae in resistance when the top gate is negatively biased. Data on the Shubnikov de Haas oscillations taken at different gate voltages show that this abrupt decrease in resistance occurs when the system changes from being double-layer to single-layer and is accompanied by transferring of electrons from the top to the bottom layer. A phenomenological model is developed to explain the transition and its dependence on the barrier width of the sample. We also find that the strength of interlayer Coulomb scattering is significantly enhanced before the transition.