Delocalization and Phase-transition in Quantum Hall Devices

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9313786 Jiang Transport experiments will be carried out on the GaAs/AlGaAs two- dimensional electron gas in the quantum Hall regime at low temperatures and high magnetic fields. The proposed experiments include study of the transport properties of the Anderson insulator in a magnetic field, investigation of the critical exponents of the phase transition between the insulator and the quantum Hall liquid, and study of the global phase diagram of the quantum Hall effect in the magnetic field-disorder plane. The delocalization processes and general scaling properties of the transitions are likely to be important to the understanding of other low dimensional quantum systems. %%% Very thin sheets of electrons can be created in artificially layered semiconductors. Such electronic two dimensional (2D) conductors have significant device potential but can also serve as ideal systems for testing recent theoretical predictions. A gate electrode can alter the character of the electron gas from that of a conductor to an insulator. An applied magnetic field can revert an insulating phase to a conducting phase. It is proposed to study the 2D electron gas as a function of applied bias and as a function of magnetic field at low cryogenic temperatures. The results will be compared to a recently published comprehensive theory. The results are expected to have an impact on the understanding of other low dimensional electronic systems. ***