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.

本研究致力于研究超薄膜在无序或磁场作用下发生超导-绝缘体转变的性质。这些薄膜是一类材料的成员，表现出由零温临界点控制的行为，零温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中的一个重要范例。表现出这种转变的其他系统包括高迁移率的二维电子气、某些磁性化合物、高T_c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，因为已经出现了相互竞争的图片。提出了一系列的电输运、隧道和结构研究，以提供这些相互竞争的理论的实验测试。这项工作的一个重要特点是将实验参数空间扩展到低温(T~20mK)和高频(f~50 GHz)，以探索转变的临界区域，这是确定其特征所必需的。此外，还将探索超导体的绝缘态，以寻找超导涨落。这项工作旨在研究在零温度和二维极限下，在无序和磁场的驱动下，超导体向绝缘体的转变。由此产生的相变是量子相变。其他表现出量子相变的材料，因此有可能在共同的理论框架内得到解释，包括多孔介质中的氦-4，高温超导体，超导结阵列，表现量子霍尔效应的二维电子气，以及各种磁性化合物。建议使用扫描隧道显微镜进行电学测量和结构研究，以提供相互竞争的理论的实验测试。这项工作在结合超低温技术、超高真空薄膜生长技术和扫描隧道显微镜方面取得了新的突破。这项工作将阐明无定形薄膜的形成，这是一个具有技术重要性的问题。对二维超导电性的理解对于理解高温超导体也是至关重要的。该项目的学生接受严格的物理和材料方面的培训，可以从事学术或工业科学方面的职业。