Strong Correlation Effects in Double Layer Two-Dimensional Electron Systems

这个实验研究项目利用双层二维电子系统来研究量子霍尔研究中的两个激动人心的主题：复合费米子(CF)和量子霍尔铁磁性(QHF)。Cf是带有两个磁性闪光量子的电子，为理解分数量子霍尔态的多样性提供了一个框架。另一方面，QHF在具有离散内部自由度(如自旋或层折射率)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中发现了显著的新现象，如织构相变和天米子拓扑激发。在双层2D电子气中，只需改变分离势垒的厚度，就可以在两个弱耦合的复合费米子液体到单个量子霍尔铁磁体之间实现内插。除了传统的磁性传输外，还将使用需要单独与各层进行电接触的新型实验探头(例如库仑阻力、隧道光谱和逆流传输)，以揭示Cf和QHF限制以及它们之间独特的转变的重要新信息。这个实验研究项目致力于研究两个导电电子系统的基本性质，每个系统被限制在一个二维平面区域内，当两个系统平行且非常接近时，只有一个薄的平面隧道势垒隔开。这种相互耦合的二维电子在低温和强磁场下表现出不同寻常的特征。在每一层中，有效的电荷载流子都是“复合费米子”，也就是带有两个磁通量子的电子。随着两层之间的间距减小，从而增加了相互作用，预计行为将从弱相互作用的复合费米子系统交叉到一种称为单量子霍尔铁磁体的状态。铁磁体是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)对另一个系统的“拖累”程度。另一方面，这些实验中使用的器件结构类似于最先进的微电子器件中使用的砷化镓技术，而事实上，制造这些器件可能会导致砷化镓技术的创新。这项研究将包括那些在物理领域接受过良好培训并熟悉半导体器件技术的学生，以及那些接受过在工业、政府或教育领域就业的优秀培训的学生。***

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. ***