Probing Exotic Phases of Two-dimensional Electrons in Unconventional Systems

摘要：固体科学与工程的主要研究领域之一是研究固体中的电子如何相互作用。这种相互作用通常会导致物质的奇异的、通常是意想不到的相。为了研究这些相和现象，重要的是要尽量减少缺陷，如杂质和缺陷。目标是通过实验探索和理解在电子系统中出现的新相，其缺陷最少。研究结果通过出版物和会议报告传达给专业以及一般的科学和工程社区。虽然这项工作的主题是基础性的，但从长远来看，这一领域的进展有利于社会，因为它可能会导致电子设备和信息处理系统的新颖，变革性概念，例如量子计算机，其操作依赖于量子和/或相互作用现象。该项目还包含了一个高质量和全面的教育组成部分，因为它包括对学生进行关键的、最先进的科学和技术领域的教育，包括高质量薄膜半导体结构的制造、表征和物理。在这些领域受过良好训练的学生对美国和世界其他国家来说都是宝贵的资源。技术摘要：本项目包括高质量、量子限制半导体结构中电子相互作用物理的实验研究。该研究包括通过分子束外延技术制造的研究，以及在电子相关现象占主导地位的低温和高磁场下的电子输运特性。工作的重点是高质量的二维电子系统局限于选择性掺杂的AlAs和双层GaAs量子阱。砷化镓中的二维电子具有与砷化镓中的标准二维电子非常不同的参数：它们具有更大的各向异性有效质量，更大的有效朗德g因子，并且它们占据多个导带谷。另一方面，GaAs双量子阱中的双层电子系统是专门设计的，因此一层的测量电子性质可以用来探测另一层的物理性质。一个例子是一个系统，其中高密度层中的复合费米子用于探测相邻低密度层中形成的维格纳晶体。因此，AlAs和双层砷化镓二维电子都为新的多体物理提供了至关重要的实验平台。本项目研究了相互作用的二维电子系统的几个奇异相；这些包括分数量子霍尔效应、复合费米子、维格纳晶体和条纹相。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical Abstract:One of the major research areas in solid-state science and engineering involves the study of how the electrons in a solid interact. The interaction often leads to exotic, often unexpected, phases of matter. To study these phases and phenomena, it is important to minimize the imperfections, such as impurities and defects. The goal is to experimentally explore and understand the new phases that arise in electron systems with the least amount of imperfections. Results of the research are communicated through publications and conference presentations to the specialized as well as general science and engineering communities. While the subject of this work is fundamental, progress in this area benefits society in the long term as it may lead to novel, transformative concepts for electronic devices and information processing systems, such as a quantum computer, whose operation relies on quantum and/or interaction phenomena. The project also incorporates a high quality and comprehensive educational component as it includes the education of students in critical, state-of-the art areas of science and technology, including the fabrication, characterization, and physics of very high-quality, thin-film semiconductor structures. Well-trained students in these fields are invaluable resources for the US as well as for the rest of the world. Technical Abstract:This project encompasses an experimental investigation of electron interaction physics in high-quality, quantum-confined semiconductor structures. The research includes studies of both fabrication, via the molecular beam epitaxy technique, and of the electronic transport properties at low temperatures and high magnetic fields where electron correlation phenomena dominate. The emphasis of the work is on high-quality two-dimensional electron systems confined to selectively-doped AlAs and bilayer GaAs quantum wells. The two-dimensional electrons in AlAs have parameters that are very different from those of the standard two-dimensional electrons in GaAs: they have a much larger and anisotropic effective mass, a much larger effective Lande g-factor, and they occupy multiple conduction band valleys. The bilayer electron systems in GaAs double quantum wells, on the other hand, are specifically designed so that the measured electronic properties of one layer could be used to probe the physics of the other layer. An example is a system where the composite fermions in a layer with high density are used to probe a Wigner crystal formed in an adjacent low-density layer. Both AlAs and bilayer GaAs two-dimensional electrons thus provide crucial and important test-beds for new many-body physics. Several exotic phases of interacting two-dimensional electron systems are studied during the course of this project; these include the fractional quantum Hall effect, composite fermions, Wigner crystal, and stripe phases.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.