9705439 Jiang This experimental research project focuses on the 2-D electron gas in the quantum Hall effect regime, specifically on the phase diagram and a localization-delocalization transition as afffected by disorder . Gated GaAs/AlGaAs devices will be used to gain control of the effective disorder of the experimental system. High magnetic field transport experiments will be carried out to study the magnetic-field-induced delocalization transition and to determine the phase diagram in the disorder-magnetic field plane. Edge-state tunneling spectroscopy will be used to probe microscopic properties and low-energy excitation of various electronic phases. %%% This experimental research project is devoted to basic properties of a conducting electron system when confined in a two-dimensional planar region. Such a confined set of electrons at low temperatures and with high magnetic fields exhibits a very unusual set of characteritics, which are of interest to theorists who wish to test and extend the basic thoery of electrons in crystalline solids. An improved theory then can be applied with more confidence to the wide range of metals and semiconductors which are of importance in microelectronics and other technologies. The experiments in this project are focusing on a "metal-insulator" transiton which ahs been observed and in particular on how it appears in connection with disorder in the environment of the electrons. On the one hand the experiments will provide new basic information about electrons when they are in interaction in confined layers at low temperatures. On the other hand the device structures which are used in these experiments are similar to those used in advanced microelectronic devices in the Gas technology. This research will involve students who will be well trained in the area of physics and will also gain familarity w ith semiconductor device technology, nd who will be excellently trained for employment in industry, government, or education. ***
