AB = 0 Conductor Insulator Transition in Two Dimensions

这个实验研究项目的重点是最近发现的二维电子气体在零磁场下的金属基态，而不是绝缘基态的性质。PI在对高迁移率硅MOSFET的电阻率测量中意外发现了金属基态，这与长期以来根据局部化理论对绝缘体的预测相反。该项目将对新发现的状态进行更详细的研究，包括磁场、温度、迁移率和导电基态的载流子密度依赖。测量将在MOSFET和GeSi异质结构器件上进行。部分测量将在美国国家科学基金会支持的佛罗里达大学的微开尔文设备中进行。这项工作有望提高对高迁移率和弱无序的稀体系中二维电子气体基态性质的理解。该实验研究项目将包括一名研究生研究员，他将在两个实验室接受优秀的培训，有利于未来在工业、政府或学术界的职业生涯。这个实验研究项目的重点是二维电子系统的性质，因为存在于一个标准的微电子器件，硅MOSFET（金属氧化物半导体场效应晶体管）的表层。该器件在栅极的控制下表现出导电，当栅极偏置为正时，将电子吸引到表面区域，在源极和漏极之间携带电流。在高迁移率MOSFET结构中，当栅极为正极时，电子存在于一个明确的平面或二维区域。该项目的PI最近在零磁场和足够低的温度下发现了这种“二维电子气体”的一个意想不到的特性。意外的发现是金属或导电状态，即使在极低的温度下。由于平面区域电势不可避免的波动，并且基于长期存在的关于电子“局域化”的理论预测，人们以前认为，温度最低的状态将是绝缘体。最近发现的金属“基态”是由PI在高迁移率硅MOSFET的电阻率测量中发现的。该项目将对新发现的金属二维基态进行更详细的研究，包括磁场、温度、迁移率和导电基态的载流子密度依赖关系。测量将在MOSFET和GeSi异质结构器件上进行。部分研究需要在接近绝对零度的毫度范围内进行测量，将在美国国家科学基金会支持的佛罗里达大学的微开尔文设备中进行。这项工作有望提高对高迁移率和弱无序的稀体系中二维电子气体基态性质的理解。该实验研究项目将包括一名研究生研究员，他将在两个实验室接受优秀的培训，有利于未来在工业、政府或学术界的职业生涯。* * *

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. ***