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》(公法111-5)资助的。*非技术摘要*二维(2D)电子系统，即电子运动被限制在平面上的系统，即2D，不仅与先进的微电子和光电子设备有关，而且是研究降维电子的重要平台。在过去的几十年里，基于半导体纳米结构(量子井)的2D电子系统揭示了大量的显著现象，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的理解。目前二维电子物理研究的一个热点是研究电子之间的强库仑相互作用如何影响系统的电子性质？？S。基于弱库仑相互作用的传统智慧认为，只要样品中有杂质，所有2D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费解的类似金属的状态。这个项目将使用热力学和隧道实验作为光谱工具来阐明金属相中2D电子系统的性质。所获得的科学结果将为解决2D电子中令人困惑的金属相和从金属到绝缘体的转变这一长期存在的问题提供新的线索。此外，这项研究将促进对当前非常感兴趣的问题的理解，例如当电子？运动之间有很强的关联性。通过对学生的教育和培训，加强国家S科技队伍建设。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，这些技能将为他们继续在学术界和工业界的职业生涯做好极好的准备。*技术摘要*二维金属-绝缘体转变(MIT)是凝聚态物理学核心的一个长期悬而未决的问题，因为2D金属态挑战了著名的定域标度理论，该理论断言所有无序的2D费米子系统在零磁场下都是局域的(绝缘的)。虽然自第一个关于硅中可能的二维费米子输运行为的报道已经过去了十多年，但对于强关联的二维费米子系统中类金属输运行为的潜在机制仍然没有达成共识。这个项目将通过重点研究金属状态的光谱研究，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道态密度(DOS)实验，以研究具有高载流子迁移率的p型砷化镓量子阱中的2D金属态。通过对2D金属的可压缩性和能量分辨隧穿DOS谱的研究，该项目将为一些广泛争论的问题带来新的见解：例如，2D金属态？一种新的物质状态？如果是这样的话，这是一种什么样的电子状态呢？该项目还将支持一名全日制研究生和几名兼职本科生研究人员。将由研究生和本科生实施的实验工作将为他们提供包括低温物理、纳米制造和低噪音实验在内的不同研究领域的全面教育和培训。这一培训将激励学生在学术界和工业界从事科学职业，并为其做好准备。

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.