AB = 0 Conductor Insulator Transition in Two Dimensions

9803440 Kravchenko这个实验研究项目集中在最近发现的金属而不是绝缘的二维电子气在零磁场中的基态。在高迁移率硅MOSFET的电阻率测量中，PI出人意料地发现了金属基态，这与定域理论对绝缘体的长期预测相反。该项目将对新发现的金属基态进行更详细的研究，包括导电基态的磁场、温度、迁移率和载流子密度的依赖关系。将在MOSFET和GeSi异质结器件上进行测量。部分测量将在佛罗里达大学由NSF支持的Microkelvin设备中进行。这项工作有望提高对具有高迁移率和弱无序的稀薄系统中二维电子气的基态性质的理解。这个实验研究项目将涉及一名研究生研究员，他将在这两个实验室地点接受出色的培训，这对未来在工业、政府或学术界的职业生涯是有益的。这个实验研究项目关注的是存在于标准微电子器件--硅MOSFET(金属氧化物半导体场效应晶体管)表层中的二维电子系统的特性。这种器件在栅电极的控制下表现出导电性，当栅电极正偏置时，会将电子吸引到表面区，在那里它们在源极和漏极之间携带电流。在高迁移率MOSFET结构中，当栅极为正时，电子存在于一个明确定义的平面或二维区域中。该项目中的PI最近发现了这样一个在零磁场和足够低的温度下的“二维电子气”的意想不到的性质。这一意想不到的发现是金属或导电状态，即使在极低的温度下也是如此。以前人们认为，由于平面区电势的不可避免的波动，以及长期以来对电子“局域化”的理论预测，最低温度状态将是绝缘体。最近在高迁移率硅MOSFET的电阻率测量中发现了金属基态。该项目将对新发现的金属二维基态进行更详细的研究，包括导电基态的磁场、温度、迁移率和载流子密度的依赖关系。将在MOSFET和GeSi异质结器件上进行测量。这项研究的一部分需要在接近绝对零度的温度范围内进行测量，将在佛罗里达大学由NSF支持的Microkelvin设施进行。这项工作有望提高对具有高迁移率和弱无序的稀薄系统中二维电子气的基态性质的理解。这个实验研究项目将涉及一名研究生研究员，他将在这两个实验室地点接受出色的培训，这对未来在工业、政府或学术界的职业生涯是有益的。***

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. ***