New Phases of Two-Dimensional Electrons in Excited Landau Levels
New Phases of Two-Dimensional Electrons in Excited Landau Levels
复制标题
激发朗道能级中二维电子的新相
DOI：
10.7907/wae0-7z77
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发表时间：
2003
影响因子：
1.1
通讯作者：
K. Cooper
中科院分区：
文献类型：
--
作者：
K. Cooper
本论文的主题是二维电子系统中一类新的集体相的实验发现和研究。实验主要涉及非常高质量的 GaAs/AlGaAs 半导体异质结构中的磁输运测量，其中大的垂直磁场用于解析电子？能谱转换为离散朗道能级。新的多体相的最引人注目的证据是仅在低于 150 mK 且在高度激发的朗道能级 N > 1 的半填充点附近观察到的巨大且前所未有的电阻各向异性。与这些各向异性状态相关的是其他新颖的电子相，其传输特征是在相同激发的朗道能级的侧面发生消失的纵向电导率。尽管让人想起众所周知的整数量子霍尔态，但绝缘相的特殊之处在于它是由电子相互作用而不是单粒子局域化驱动的。基于高朗道能级中“条纹”和“气泡”电荷密度波形成的有说服力的理论图景可以解释许多实验结果。例如，条带态方向对称性的破坏可能是观察到的输运各向异性的基础，而无序引起的气泡晶格的钉扎可能会导致高朗道能级的绝缘区域。对各向异性传输特性的进一步研究阐明了所谓的条纹相可能的对称破缺机制，并提供了证据表明条纹可以更准确地描述为量子电子液晶。此外，涉及高压偏置下绝缘区域击穿的实验可能表明气泡相发生脱钉转变。这些结果激发了人们对二维相关电子系统领域的浓厚兴趣，并可能表明凝聚态物质系统中仍有多种新现象有待发现。
The subject of this dissertation is the experimental discovery and investigation of a new class of collective phases in two-dimensional electron systems. The experiments mainly involve magnetotransport measurements in very high quality GaAs/AlGaAs semiconductor heterostructures, where a large perpendicular magnetic field serves to resolve the electrons? energy spectrum into discrete Landau levels. The most dramatic evidence of a new many-body phase is the huge and unprecedented resistance anisotropy observed only below 150 mK and around the half-filling points of the highly excited Landau levels N > 1. Associated with these anisotropic states are other novel electron phases whose transport signature is a vanishing longitudinal conductivity occurring in the flanks of the same excited Landau levels. Although reminiscent of the well-understood integer quantum Hall states, the insulating phases are exceptional for being driven by electron interactions rather than single-particle localization. A persuasive theoretical picture based on "stripe" and "bubble" charge density wave formation in high Landau levels can account for many of the experimental results. For example, the broken orientational symmetry of the stripe state may underlie the observed transport anisotropy, while disorder-induced pinning of the bubble lattice could give rise to the insulating regions in high Landau levels. Further investigation of the anisotropic transport characteristics has elucidated possible symmetry-breaking mechanisms of the purported stripe phase and has provided evidence that the stripes may be more accurately described as a quantum electronic liquid crystal. In addition, experiments involving the breakdown of the insulating regions at high voltage biases may point to a depinning transition of the bubble phase. These results have spurred intense interest in the field of correlated electron systems in two dimensions and may be an indication of the variety of new phenomena in condensed matter systems still awaiting discovery.