Elucidating the Anomalous Metallic State in Strongly Correlated Two-D Fermions with Density of States Measurements

该奖项是根据2009年美国复苏和再投资法案（公法111 - 5）资助的。二维（2D）电子系统，其中电子的运动被限制在一个平面（即2D）内的系统，不仅与先进的微电子和光电器件相关，而且也是在减小的维度中研究电子的重要平台。在过去的几十年里，基于半导体纳米尺度结构（量子威尔斯）的二维电子系统已经揭示了大量的显着现象，这些现象导致了许多发现，并随后对物质的各种量子态有了更深入的理解。目前二维电子物理研究的一个焦点是研究电子之间的强库仑相互作用对系统的影响。的电子性质。基于弱库仑相互作用的传统观点认为，只要样品中存在杂质，所有二维电子系统都是绝缘体。然而，最近的实验表明，如果电子之间的库仑相互作用很强，2D电子可以显示出令人困惑的金属样状态。本计画将利用热力学与穿隧实验作为光谱工具，以阐明金属相中二维电子系统的性质。所获得的科学结果将为长期存在的令人困惑的金属相和二维电子中的金属到绝缘体转变问题提供新的线索。此外，这项研究还将促进对当前非常感兴趣的问题的理解，例如当电子？运动彼此强烈相关。通过教育和培训学生，这个项目将加强国家？中国的科技劳动力。该项目将支持一名全日制研究生攻读博士学位，并将培训兼职本科生。研究生和本科生将获得实验室技能，这将为他们继续在学术界和工业界的职业生涯做好准备。技术摘要 * 二维（2D）中的金属-绝缘体转变（MIT）是凝聚态物理学核心的长期未解决的问题，因为2D金属状态挑战了著名的定域化标度理论，该理论断言所有无序的2D费米子系统在零磁场下都是定域化的（绝缘的）。虽然从硅中可能的2D MIT的第一次报道以来已经过去了十多年，但是对于强关联2D费米子系统中金属类输运行为的潜在机制仍然没有达成共识。该项目将通过专注于金属状态下的光谱研究，在新的战线上解决这个问题。除了常规的输运测量外，还将进行热力学和隧穿态密度（DOS）实验，以研究具有高载流子迁移率的p型砷化镓量子威尔斯中的二维金属态。通过研究二维金属的可压缩性和能量分辨隧穿态密度谱，该项目将对一些广泛争论的问题产生新的见解：例如，二维金属态？一种新的物质状态如果是这样的话，它是一种什么样的电子状态？该项目还将支持一名全职研究生和几名兼职本科生研究人员。由研究生和本科生实施的实验工作将为他们提供不同研究领域的综合教育和培训，包括低温物理，纳米纤维和低噪声实验。这项培训将激励学生为学术界和工业界的科学事业做好准备。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).**** NON-TECHNICAL ABSTRACT****Two-dimensional (2D) electron systems, systems where the motion of the electrons is confined to a plane, i.e. 2D, are not only relevant to advanced microelectronic and optoelectronic devices, but also important platforms in the study of electrons in reduced dimensions. In the past few decades, 2D electron systems based on semiconductor nano-scale structures (quantum wells) have revealed a plethora of remarkable phenomena which have led to many discoveries and subsequently a deeper understanding of various quantum states of matter. A current focal point in 2D electron physics research is the study of how the strong Coulomb interaction between electrons influences the system?s electronic properties. Conventional wisdom based on weak Coulomb interaction asserts that all 2D electron systems are insulators as long as there are impurities in the sample. However, recent experiments have shown that 2D electrons can show a puzzling metal-like state if the Coulomb interaction between electrons is strong. This project will employ thermodynamic and tunneling experiments as spectroscopic tools to elucidate the nature of 2D electron systems in the metallic phase. The scientific results obtained will shed new light on the long standing problems of the puzzling metallic phase and metal-to-insulator transition in 2D electrons. In addition, this research will advance understanding of current questions of great interest, such as what happens to the properties of a material when the electrons? motions are strongly correlated with each other. Through educating and training students, this project will strengthen the nation?s workforce in science and technology. This project will support a full time graduate student towards his/her PhD degree and will also train part time undergraduate students. Graduate and undergraduate students will gain laboratory skills that will be excellent preparation for them to continue toward career in both academia and industry.**** TECHNICAL ABSTRACT****The metal-insulator transition (MIT) in two dimensions (2D) is a long- standing unsolved problem at the heart of condensed matter physics, as a 2D metallic state challenges the celebrated scaling theory of localization which asserts that all disordered 2D Fermion systems are localized (insulating) at zero magnetic field. Although more than ten years have passed since the first report of a possible 2D MIT in silicon, there is still no consensus on the underlying mechanism of the metallic-like transport behavior in strongly correlated 2D Fermion systems. This project will tackle the problem on new fronts by focusing on spectroscopic studies in the metallic state. Both thermodynamic and tunneling density of states (DOS) experiments will be performed in addition to the conventional transport measurements to study the 2D metallic state in p-type gallium arsenide quantum wells with high carrier mobility. Through investigating the compressibility and energy-resolved tunneling DOS spectra of the 2D metal, this project will lead to new insights to some widely debated questions: e.g. is the ?2D metallic state? a new state of matter? If so, what kind of electronic state of matter is it? This project will also support a full time graduate student and several part time undergraduate researchers. The experimental work to be implemented by the graduate and undergraduate students will provide them a comprehensive education and training in different research areas including low-temperature physics, nanofabrication and low-noise experimentation. This training will motivate and prepare the students for scientific careers in both academia and industry.