Anomalous Metal in Two Dimensions

这个实验和理论项目将解决在20世纪90年代初S在零磁场中观察到的低密度高迁移率二维电子气中的强烈的类似金属的温度依赖性。如果这种效应实际上是2D(2D MIT)中的金属-绝缘体相变，则局域化的单参数标度理论将被违背。尽管进行了密集的努力，但即使是2D麻省理工学院的最基本功能也还不清楚。这项研究集中在两个相互关联的关键问题上：(A)“金属”状态下的电阻率的反常温度依赖性的起源；(B)“金属”状态下相互作用电子的基态的性质。计划进行一系列输运和热力学测量，以区分该现象的两种主要情景：零温度量子相变和有限温度交叉，这是由于散射时间的温度相关性。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~20mK)。罗格斯大学的实验研究与佛罗里达大学的理论工作相辅相成。虽然这项提案的主要重点是基本主题，但在高迁移率硅和硅锗结构中的输运方面的一些预期结果预计将对广泛的应用产生影响。参与该项目的研究生接受具有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成为绝缘体。最近，对金属状态的观察对这一理论提出了挑战，首先是在高迁移率的硅场效应晶体管中，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。由于强烈的电子-电子相互作用(零温度量子相变)，意外的金属态可能是新基态的证据。也有人提出了其他解释，包括基于无序的温度依赖性、载流子通过宏观不均匀的渗流等。这个理论和实验相结合的项目旨在通过进行各种输运和热力学测量，在两个维度上建立这种新的金属状态的真实性质。为了拓展实验参数的空间，前沿的超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与佛罗里达大学的理论工作一起进行。参与这项研究的学生接受了先进实验技术的严格培训，并为在学术或工业环境中就业做好了准备。

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.