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

w：\awards\awards96\*.doc 9801983 Valles This 实验研究项目涉及 机制 的 的 超导绝缘体 量子 在超薄淬火凝聚金属膜中表现出相变。 这种转变可能发生在无序超导膜如此之薄，以至于其每平方的正常电阻为h/4 e ~ 2的数量级，并且绝缘体状状态也被磁场促进。该研究项目包括在低温基底上原位蒸发超薄层，以及原位测量 的 磁输运， STM 地形 和光谱学。我们的目标是建立之间的相关性的宏观运输表现出的SIT过渡和微观性能所揭示的STM测量。要解决的一个关键问题是在过渡附近的超导序参量的相位和振幅波动的相对重要性。 这个研究项目 它是跨学科性质的，通常有几个本科生和研究生参与其活动。 这些参与有利于学生为进一步的学习做好准备。 研究 和 的职业生涯 工业， 政府实验室或学术界。 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性。 如果金属是超导体，如铅，通常的行为是在金属状态和超导状态之间的转变，即金属膜的电阻将在转变温度以下变为零。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，其中在绝缘状态和超导状态之间发生转变。 这种不寻常的行为是这个项目的重点。 该实验装置允许真空存款的金属层到液氦温度的基板上，所谓的淬火冷凝，这允许超薄和均匀厚度的薄膜，显示出感兴趣的效果。 搭建了实验装置 到 允许在同一设备中进行膜的电阻测量，并且还允许在不干扰所沉积的金属膜的情况下进行扫描隧道显微镜形貌图和电测量。温度和磁场也可以变化。这项基础研究的目标是了解不寻常的绝缘体-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电传导的整体理解。该研究计划是跨学科的性质，通常涉及几个本科生和研究生在其活动。 这些参与有利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。 ***

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. ***