AB = 0 Conductor Insulator Transition in Two Dimensions

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w:\awards\awards96\*.doc 9803440 Kravchenko This experimental research project focuses on the properties of the recently discovered metallic, rather than insulating, ground state of the two dimensional electron gas in zero magnetic field. The unexpected discovery of a metallic ground state, contrary to a long-standing prediction of an insulator by localization theory, was made by the PI in resistivity measurements on high mobility silicon MOSFET's. This project will subject the newly discovered state to more detailied studies, including the magnetic field, temperature, mobility, and carrier-density dependences of the conducting ground state. Measurements will be made on MOSFET's and on GeSi heterostructure devices. Portions of the measurements will be made at the NSF-supported Microkelvin Facility at the University of Florida. The work is expected to improve understanding of the ground state properties of the 2-D electron gas, in dilute systems with high mobility and weak disorder. This experimental research project will involve a graduate student researcher who will receive excellent training at both laboratory locations, beneficial to a future career in industry, government or academia. %%% This experimental research project is focuses on the properties of a two-dimensional electron system, as exists in the surface layer of a standard microelectronics device, the silicon MOSFET (Metal Oxide Semiconductor Field Effect Transistor). This device exhibits conduction under the control of the gate electrode, which, when biased positively, draws electrons to the surface region, where they carry a current between the source and drain electrodes. In high mobility MOSFET structures, the electrons, when the gate is positive, exist in a well defined region, which is planar or two dimensional. The PI's in the project have recently discovered an unexpected property of such a "two dimensional electron gas" in zero magnetic field and at sufficiently low temperature. The unexpected discovery is of a metallic or conducting state, even at extremely low temperature. It had previously been thought, due to unavoidable fluctuations in the electric potential in the planar region, and based on a long-standing theoretical prediction of "localization" of the electrons, that the lowest temperature state would be an insulator. The recent discovery of the metallic "ground state" was made by the PI in resistivity measurements on high mobility silicon MOSFET's. This project will subject the newly discovered metallic 2-D ground state to more detailied studies, including the magnetic field, temperature, mobility, and carrier-density dependences of the conducting ground state. Measurements will be made on MOSFET's and on GeSi heterostructure devices. Portions of the research, which require measurements in the millidegree range close to absolute zero temperature, will be made at the NSF- supported Microkelvin Facility at the University of Florida. The work is expected to improve the understanding of the ground state properties of the 2-D electron gas, in dilute systems with high mobility and weak disorder. This experimental research project will involve a graduate student researcher who will receive excellent training at both laboratory locations, beneficial to a future career in industry, government or academia. ***