Anomalous Metal in Two Dimensions

这个实验和理论项目将解决强;金属一样的电阻率的温度依赖性，这是在20世纪90年代初观察到的低密度和高迁移率的二维电子气在零磁场。 如果这种效应实际上是二维的金属-绝缘体转变（2D MIT），则将违反局域化的单参数标度理论。 尽管进行了大量的努力，但即使是2D MIT的最基本特征也尚未被理解。 本研究集中在两个相互关联的关键问题：（a）在“金属”状态的电阻率的异常温度依赖性的起源，和（B）在“金属”状态的相互作用电子的基态的性质。 一套运输和热力学测量计划，应区分两个主要的情况下的现象：零温度量子相变与有限温度交叉由于散射时间的温度依赖性。 这项工作的一个重要特点是将实验参数空间扩展到最低可达温度（T ~ 20 mK）。罗格斯大学的实验研究得到了佛罗里达大学理论工作的补充。 虽然该提案的主要重点是基本主题，但预计高迁移率硅和硅锗结构中的传输的一些预期结果将对广泛的应用产生影响。参与该项目的研究生将接受尖端技术的基本实验技术培训。根据无序导体中电子的传统理论，二维导体在足够低的温度下最终会变成绝缘体。 这一理论最近受到了金属态的观察的挑战，首先是在高迁移率硅场效应晶体管中，后来在许多其他二维结构中。 这种金属状态是由载流子密度的变化驱动的。 这个意想不到的金属态可能是由于强电子-电子相互作用（零温度量子相变）而产生的新基态的证据。 其他的解释也被建议，包括那些基于温度依赖性的障碍，通过宏观不均匀性的载体渗透等，这种结合的理论和实验项目的目的是建立在两个维度的新的金属状态的真实性质，通过进行各种运输和热力学测量。 为了扩大实验参数的空间，尖端的超低温低温技术将与新颖的纳米光刻技术相结合。 罗格斯大学的实验研究是与佛罗里达大学的理论工作一起进行的。 参与这项研究的学生接受先进实验技术的严格培训，并为学术或工业环境中的职业生涯做好准备。

This experimental and theoretical project will address the strong; metal-like temperature-dependence of the resistivity, that was observed in the early 1990's in a low-density and high-mobility two-dimensional electron gas in zero magnetic field. If this effect is actually a metal-insulator transition in 2D (2D MIT), the one-parameter scaling theory of localization would be violated. Despite intensive efforts, even the most basic features of the 2D MIT are not yet understood. This research is focused on two interrelated key issues: (a) the origin of the anomalous temperature dependence of the resistivity in the "metallic" state, and (b) the nature of the ground state of interacting electrons in the "metallic" state. A suite of transport and thermodynamic measurements is planned that should distinguish between two major scenarios of the phenomenon: a zero-temperature quantum phase transition versus a finite-temperature crossover due to the temperature dependence of the scattering time. An important feature of the work is the extension of the experimental parameter space down to the lowest accessible temperatures (T ~ 20mK). The experimental studies at Rutgers University are supplemented by the theoretical work at University of Florida. Whereas the main focus of this proposal is on fundamental topics, some anticipated results on transport in high-mobility silicon and silicon-germanium structures are expected to have an impact on a broad spectrum of applications. Graduate students involved in the project receive training in fundamental experimental techniques with cutting edge technology. %%%According to the conventional theory of electrons in disordered conductors, two-dimensional conductors eventually become insulators at sufficiently low temperatures. This theory has been challenged recently by observations of a metallic state, first in high-mobility silicon field-effect transistors, and later in a number of other two-dimensional structures. This metallic state is driven by changes in the carrier density. The unexpected metallic state might be an evidence for a new ground state owing to strong electron-electron interactions (the zero-temperature quantum phase transition). Other explanations have also been suggested including those based on the temperature dependence of disorder, percolation of carriers through macroscopic inhomogeneities, etc. This combined theory and experiment project is aimed at establishing the true nature of the novel metallic state in two dimensions by carrying out a variety of transport and thermodynamic measurements. In order to expand the space of experimental parameters, cutting-edge ultra-low-temperature cryogenic technologies will be combined with novel nano-lithographic techniques. The experimental studies at the Rutgers University are conducted in conjunction with the theoretical work at the University of Florida. Students involved in this research receive rigorous training in advanced experimental techniques, and are prepared for careers in either academic or industrial environment.