Strong Correlation Effects in Double Layer Two-Dimensional Electron Systems

w：\awards\awards96\num.doc 9700945 Eisenstein 本实验研究计画利用双层二维电子系统，研究量子霍尔研究中两个令人兴奋的课题：复合费米子（CF）和量子霍尔铁磁性（QHF）。CF的，这是电子与两个磁通 广达 连接， 提供 一 框架 来理解分数量子霍尔态的多样性。 另一方面，QHF在具有离散内部自由度（如自旋或层指数）的系统中的量子化霍尔态与普通磁性材料之间提供了一个美丽而有用的类比。在QHF中发现了许多新的现象，如织构相变和Skyrmionic拓扑激发。在双层2D电子气体中，简单地改变 的 隔离屏障的厚度 允许在最好描述为两个弱耦合复合费米子液体的系统与单个量子霍尔铁磁体之间进行插值。除了常规的磁输运之外，需要与各个层（例如，库仑阻力，隧穿光谱，和逆流运输）将被用来揭示重要的新信息，在CF和QHF限制，独特的，对它们之间的过渡。 这个实验研究项目致力于两个导电电子系统的基本特性，每个系统都被限制在一个二维平面区域中，当两个系统平行并且非常接近时，仅由一个薄的平面隧道势垒分开。 这种二维电子在低温和高磁场下的耦合平行组表现出不寻常的特性。在每一层中，有效的载流子是“复合费米子”，它是电子与两个磁通量量子连接。 为 当两个层之间的间距减小，这增加了相互作用时，预期从弱相互作用复合费米子系统的情况到称为单量子霍尔铁磁体的状态的行为交叉。 铁磁体是一种电子磁矩平行排列的系统，如条形磁铁或指南针。 一方面，这些实验将提供有关低温下电子系统在受限层中相互作用的新的基本信息。例如，一个实验将测量一个系统中的运动（电流）“拖动”第二个系统的程度。另一方面，在这些实验中使用的器件结构类似于GaAs技术中最先进的微电子器件中使用的结构，并且实际上制造这些器件可能导致GaAs技术的创新。这项研究将涉及学生谁会很好 在物理学领域受过训练，也将熟悉半导体器件技术，并将在工业，政府或教育部门接受出色的培训。 ***

w:\awards\awards96\num.doc 9700945 Eisenstein This experimental research project utilizes double layer two- dimensional electron systems to study two exciting topics in quantum Hall research: composite Fermions (CF) and quantum Hall ferromagnetism (QHF). CF's, which are electrons with two magnetic flulx quanta attached, have provided a framework for understanding the diversity of fractional quantum Hall states. QHF, on the other hand, offers a beautiful and useful analogy between quantized Hall states in systems with discrete internal degrees of freedom (like spin or layer index) and ordinary magnetic materials. Remarkable new phenomena, like textural phase transitions and skyrmionic topological excitations, have been discovered in QHF's. In double layer 2D electron gases, simply changing the thickness of the separating barrier allows interpolation between a system best described as two weakly coupled composite fermion liquids to a single quantum Hall ferromagnet. In addition to conventional magneto-transport, novel experimental probes requiring separate electrical contact to the individual layers (e.g., Coulomb drag, tunneling spectroscopy, and counterflow transport) will be employed to uncover important new information in both the CF and QHF limits and, uniquely, on the transition between them. %%%% This experimental research project is devoted to basic properties of two conducting electron systems, each confined into a two- dimensional planar region, when the two systems are parallel and in close proximity separated only by a thin planar tunnel barrier. Such coupled parallel sets of two-dimensional electrons at low temperatures and with high magnetic fields exhibit unusual characteristics. In each layer the effective charge carriers are "composite Fermions", which are electrons with two magnetic flux quanta attached. As the spacing between the two layers is reduced, which increases the interaction, a crossover in behavior is expected from a case of weakly interacting composite Fermion systems to a state called a single quantum Hall ferromagnet. A ferromagnet is a system in which electron magnetic moments are aligned parallel, as in a bar magnet or compass needle. On the one hand the experiments will provide new basic information about electron systems when they are in interaction in confined layers at low temperatures. For example, one experiment will measure the degree to which motion (electrical current) in one system "drags" the second system. On the other hand the device structures which are used in these experiments are similar to those used in the most advanced microelectronic devices in the GaAs technology, and indeed fabricating these devices may lead to innovation in the GaAs technology. This research will involve students who will be well trained in the area of physics and will also gain familiarity with semiconductor device technology, and who will be excellently trained for employment in industry, government, or education. ***