Tunneling and Transport in Ordered and Disordered Superconductors

有序和无序超导体中的隧道效应和输运

• 批准号: 9876816
• 负责人: Allen Goldman
• 金额: $ 42万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-04-01 至 2002-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9876816&HistoricalAwards=false
• 关键词: Tunneling; Transport; Ordered; Disordered; Superconductors

9876816GoldmanThis research is focussed on the investigation of the properties of ultra-thin films, which undergo superconductor-insulator transitions controlled by disorder or magnetic field. These films are members of a class of materials exhibiting behavior governed by a zero-temperature critical point, which separates two distinct quantum mechanical ground states. Such quantum phase transitions are an important paradigm in contemporary Condensed Matter Physics. Among other systems exhibiting such transitions are high-mobility two-dimensional electron gases, certain magnetic compounds, high-Tc superconductors, and liquid helium adsorbed on random substrates. The underlying physical model of the superconductor-insulator transition is unresolved, as competing pictures have been developed. A series of electrical transport, tunneling and structural investigations are proposed to provide experimental tests of these competing theories. An important feature of the work is the extension of the experimental parameter space to low temperatures (T ~ 20mK) and high frequencies (f ~ 50 GHz) so as to explore the critical regime of the transition, which is essential to determining its character. Also the insulating state will be probed in search of superconducting fluctuations.%%%This work is directed at the study of the transition of superconductors into insulators, driven by disorder and magnetic field, at the limits of zero temperature and two dimensions. The resultant phase transitions are quantum transitions. Other materials exhibiting quantum phase transitions, and thus potentially explainable within a common theoretical framework, include helium-4 in porous media, high temperature superconductors, superconducting junction arrays, two-dimensional electron gases exhibiting the quantum Hall effect, and various magnetic compounds. Electrical measurements and structural investigations using scanning tunneling microscopy are proposed to provide experimental tests of competing theories. The work breaks new ground in combining ultra-low temperature cryogenic technology, ultra-high vacuum thin film growth techniques, and scanning tunneling microscopy. The work will shed light on the formation of amorphous films, a problem of technological importance. The understanding of superconductivity in two dimensions is also critical to the understanding of high temperature superconductors. Students in this program receive rigorous training in physics and materials, and can pursue careers in either academic or industrial science.

9876816戈德曼这项研究的重点是研究超薄膜的性质，它经历由无序或磁场控制的超导体-绝缘体转变。这些薄膜是一类表现出由零温度临界点控制的行为的材料的成员，该临界点将两个不同的量子力学基态分开。这种量子相变是当代凝聚态物理学的一个重要范式。在其他表现出这种转变的系统中，有高迁移率的二维电子气、某些磁性化合物、高Tc超导体和吸附在随机衬底上的液氦。超导体-绝缘体转变的基本物理模型尚未解决，因为已经开发了相互竞争的图片。提出了一系列的电传输，隧道和结构的调查，这些竞争理论提供实验测试。该工作的一个重要特点是将实验参数空间扩展到低温（T ~ 20 mK）和高频（f ~ 50 GHz），以探索转变的临界状态，这对于确定其特征至关重要。此外，绝缘状态将被探测，以寻找超导波动。这项工作旨在研究在零温度和二维极限下，由无序和磁场驱动的超导体向绝缘体的转变。由此产生的相变是量子跃迁。其他表现出量子相变的材料，因此可能在一个共同的理论框架内解释，包括多孔介质中的氦-4，高温超导体，超导结阵列，表现出量子霍尔效应的二维电子气，以及各种磁性化合物。电测量和结构调查，使用扫描隧道显微镜提出了竞争理论提供实验测试。这项工作在结合超低温冷冻技术、超高真空薄膜生长技术和扫描隧道显微镜方面开辟了新天地。这项工作将阐明非晶薄膜的形成，这是一个重要的技术问题。理解二维超导性对于理解高温超导体也至关重要。该计划的学生接受严格的物理和材料培训，并可以从事学术或工业科学的职业。