Single-layer transport measurements of bilayer 2D electron and hole systems in GaAs heterostructures

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Copyright: Ho, Lap-hang
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Abstract
In this thesis we have studied bilayer two-dimensional (2D) electron and hole systems in GaAs. The work consists of three experimental studies, which involve low temperature magneto-transport measurements of one 2D system independent of the other, and one theoretical study. Firstly, we present a new technique for measuring the chemical potential of a 2D system. In a bilayer 2D electron system (2DES), we use the lower 2DES as a quantum Hall electrometer to measure the chemical potential of the upper 2DES. We track the evolution of the Landau levels in the upper 2DES, and extract an effective mass that is consistent with previous values. Secondly, we investigated the hysteresis in the quantum Hall regime of a bilayer 2DES, which was previously attributed to a slow charge transfer mechanism between the adjacent layers. Using our quantum Hall electrometry technique, we provide compelling evidence that the origin of the hysteresis is instead the nonequilibrium induced currents that are generated in one of the 2DES at integer filling factors. Thirdly, we present a technique for using a nearby ground plane to screen the long-range Coulomb interactions in a 2D hole system (2DHS). Using a bilayer 2DHS, we are able to vary the distance from the ground plane to the 2DHS between 50 and 340nm, in the same sample without thermal cycling. This technique was used to study the effect of a ground plane on the metallic behaviour, which arises from electron-electron interactions, and it was shown that the ground plane screening effect was much weaker than might at first be expected. Finally, we developed a theoretical model to answer some important questions raised by the ground plane screening experiment: Does a 2D system perform ground plane screening as effectively as a metal gate? How effective do we expect ground plane screening to be when the 2D system is in the metallic regime? We show that ground plane screening by a 2D system is at least as effective as a metal gate, and that the intralayer screening when a 2D system is in the metallic regime dominates the ground plane screening effect.
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Author(s)
Ho, Lap-hang
Supervisor(s)
Micolich, Adam
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Publication Year
2010
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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