Tunneling and Transport Studies of Strongly Disordered Ultra-Thin Films of Metals and Superconductors

金属和超导体强无序超薄膜的隧道和输运研究

• 批准号: 9801983
• 负责人: James Valles
• 金额: $ 27万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-07-01 至 2002-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9801983&HistoricalAwards=false
• 关键词: Tunneling; Transport; Studies; Strongly; Disordered

w:\awards\awards96\*.doc 9801983 Valles This experimental research project is concerned with the mechanism of the superconductor-insulator quantum phase transition exhibited in ultra-thin quench condensed metal films. Such a transition may occur for a disordered superconducting film so thin that its normal resistance per square is on the order of h/4e2, and the insulator like state is also promoted by a magnetic field. The research project involves in-situ evaporation of ultra thin layers onto cryogenic substrates, and in-situ measurements of magnetotransport, STM topography and spectroscopy. The goals are to establish correlations between the macroscopic transport exhibiting the SIT transition and the microscopic properties as revealed by the STM measurements. A key issue to resolve is the relative importance of phase and amplitude fluctuations of the superconducting order parameter in the vicinity of the transition. This research program is interdisciplinary in nature and has typically involved several undergraduate and graduate students in its activities. These involvements are beneficial in the preparation of students for further study and for careers in industry, government laboratories or academia. %%% This experimental research project is concerned with electrical conduction in extremely thin layers of metal, at very low temperature. If the metal is a superconductor, like lead, the usual behavior is a transition between a metallic state and a superconducting state, that is the resistance of the metal film will go to zero below a transition temperature. However, when the films are only a few atomic layers thick, an entirely different behavior can be observed, in which a transition occurs between an insulating state and a superconducting state. This unusual behavior is the focus of this project. The experimental apparatus allows vacuum deposit of a metal layer onto a liquid-helium- temperature substrate, so called quench condensing, which permits the ultra thin and even-thickness films that show the effect of interest. The experimental apparatus is set up to allow electrical resistance measurements of the film to be made in the same apparatus, and also scanning tunneling microscope topographs and electrical measurements to be made without disturbing the as deposited metal film. The temperature and magnetic field can also be varied. The goal of this basic research is to understand the mechanism of the unusual insulator-superconductor transition. Such understanding will add to the overall understanding of electrical conduction in materials and also in microelectronic and other devices. This research program is interdisciplinary in nature and has typically involved several undergraduate and graduate students in its activities. These involvements are beneficial in the preparation of students for further study and for careers in industry, government laboratories or academia. ***

这个实验研究项目涉及超薄淬火凝聚金属薄膜中超导体-绝缘体量子相变的机制。这种转变可能发生在这样一种无序超导薄膜上，这种无序超导薄膜很薄，其每平方法向电阻约为h/4e2量级，并且类绝缘体状态也受到磁场的促进。该研究项目包括在低温衬底上原位蒸发超薄层，以及对磁传输、扫描隧道显微镜形貌和光谱学的原位测量。我们的目标是建立呈现SIT转变的宏观输运与STM测量揭示的微观性质之间的关联。一个需要解决的关键问题是超导序参数的相位和幅度涨落在相变附近的相对重要性。这个研究项目本质上是跨学科的，通常有几个本科生和研究生参与到它的活动中。这些参与有助于学生为进一步学习和在工业、政府实验室或学术界的职业生涯做好准备。这个实验研究项目是关于极薄金属层在极低温度下的导电。如果金属是超导体，比如铅，通常的行为是金属状态和超导状态之间的转变，也就是说，在转变温度以下，金属膜的电阻将变为零。然而，当薄膜只有几个原子层厚时，可以观察到完全不同的行为，在绝缘态和超导态之间发生转变。这种不寻常的行为是这个项目的重点。该实验装置允许在液氦温度的衬底上真空沉积一层金属层，即所谓的淬火冷凝，这种冷凝允许显示出感兴趣的超薄、均匀厚度的薄膜。建立的实验装置允许在相同的装置中进行薄膜的电阻测量，还可以在不干扰沉积的金属膜的情况下进行扫描隧道显微镜的形貌和电学测量。温度和磁场也可以改变。这项基础研究的目的是了解这种不寻常的绝缘体-超导体转变的机制。这样的理解将增加对材料以及微电子和其他器件中的导电性的整体理解。这个研究项目本质上是跨学科的，通常有几个本科生和研究生参与到它的活动中。这些参与有助于学生为进一步学习和在工业、政府实验室或学术界的职业生涯做好准备。***