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.

9876816GoldManthis Thine研究的重点是研究超薄膜的性质，该薄膜经历了由无序或磁场控制的超导体 - 绝缘体转变。这些薄膜是由零温临界点控制的一类材料的成员，该材料将两个不同的量子机械基态分开。这种量子相变是当代冷凝物理物理学的重要范式。在其他表现出此类过渡的系统中，有二维电子气体，某些磁性化合物，高-TC超导体以及吸附在随机底物上的液态氦气。由于已经开发了竞争图片，因此无法解决超导体 - 绝缘体过渡的基本物理模型。提出了一系列电气传输，隧道和结构研究，以提供这些竞争理论的实验测试。这项工作的一个重要特征是将实验参数空间扩展到低温（T〜20MK）和高频（F〜50 GHz），以探索过渡的临界状态，这对于确定其特征至关重要。同样，将探测绝缘状态以寻找超导波动。%%％％;这项工作针对零温度和两个维度的限制，在零温度和两个维度的范围内研究超导体向绝缘体的过渡。结果相变是量子转变。表现出量子相变的其他材料，因此在共同的理论框架内可以解释，包括多孔培养基中的氦4，高温超导体，超导连接阵列，二维电子气体表现出量子厅效应，以及各种磁性化合物。提出了使用扫描隧道显微镜进行的电测量和结构研究，以提供竞争理论的实验测试。这项工作打破了新的地面，结合了超低温度低温技术，超高真空薄膜生长技术和扫描隧道显微镜。这项工作将揭示出无定形膜的形成，这是技术重要性的问题。对二维中超导性的理解对于理解高温超导体也至关重要。该计划的学生接受了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。