9701426 Tsui This research is in the area of semiconductor physics, probing the behavior of electrons forming a 2-D gas in extremely high mobility semiconductor devices. The research is in the area of the Quantum Hall Effect (QHE) and the Fractional Quantum Hall Effect. The PI in recent research has contributed to dicovery of a duality symmetry. The proposed research aims to explore the duality symmetry between the QHE liquid phase and the newly discovered insulating phase. Another topic to be studied is the universal relation between the longitudinal and transverse conductivity in QHE liquid to insulator transition. Another class of transitions is proposed in extremely low mobility samples. %%% This research project experimentally studies the behavior of conduction electrons in state-of-the-art semiconductor devices. It is found that conduction electrons n extremely pure semiconductor samples, when confined to move in a nearly two dimensional planar region, at low temperatures and high transverse magnetic field, behave in unique ways. These previously observed effects are known as the Quantum Hall Effect and the Fractional Quantum Hall Effect. They are basic effects resulting from the laws of quantum mechanics applied to a dense gas of electrons interacting with each other by Coulomb repulsion. New behaviors are expected, described as new phases of the electron gas, and this research is devoted to finding and describing these new behaviors. The understanding gained can be expected to contribute to improvements in microelectronic device technology. ***
