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. ***

W：\ Awards \ Awards96 \*。DOC 9801983 VALLES这个实验研究项目涉及超固定淬灭金属膜中表现出的超导体 - 绝缘体量子相变的机制。 对于无序的超导膜可能会发生这种过渡，以至于其每个正方形的正常电阻在H/4E2的顺序上，并且像状态这样的绝缘体也通过磁场促进。该研究项目涉及将超薄层的原位蒸发到低温底物上，以及磁转运，STM地形和光谱法的原位测量。目的是建立表现出位置转变的宏观运输与STM测量结果所揭示的微观特性之间的相关性。解决的关键问题是过渡附近超导顺序参数的相位和振幅波动的相对重要性。 该研究计划本质上是跨学科的，通常涉及几个本科生和研究生的活动。 这些参与对学生的准备以及行业，政府实验室或学术界的职业有益。 该实验研究项目与在非常低的温度下极薄的金属层中的电导有关。 如果金属是像铅这样的超导体，则通常的行为是金属状态和超导状态之间的过渡，即金属膜的抗性将达到低于过渡温度的零。但是，当膜只有几个原子层厚时，就可以观察到完全不同的行为，其中绝缘状态和超导状态之间发生过渡。 这种不寻常的行为是该项目的重点。 实验设备允许将金属层真空沉积在液氧温度底物上，即所谓的淬灭凝结，这允许超薄且均匀的膜显示出感兴趣的效果。 设置实验设备以允许在同一设备中制成膜的电阻测量，还可以扫描隧道显微镜地形图和电气测量值，而不会干扰AS沉积金属膜。温度和磁场也可以变化。这项基础研究的目的是了解不寻常的绝缘体 - 渗透导体过渡的机制。 这种理解将增加对材料以及微电子和其他设备电气传导的总体理解。该研究计划本质上是跨学科的，通常涉及几个本科生和研究生的活动。 这些参与对学生的准备以及行业，政府实验室或学术界的职业有益。 ***