Transport and Magnetic Properties of NS Structures

NS 结构的输运和磁性

• 批准号: 9801982
• 负责人: Venkat Chandrasekhar
• 金额: $ 22.3万
• 依托单位: Northwestern 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: 1998-09-01 至 2002-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9801982&HistoricalAwards=false
• 关键词: Transport; Magnetic; Properties; NS; Structures

9801982 Chandrasekhar This experimental condensed matter physics project addresses the fabrication and characterization of normal metal (N) - superconductors (S) structures whose dimensions are comparable to the fundamental coherence lengths in such materials. The electrical conductance and other properties of these nanostructures are predicted, and observed, to display non-classical and surprising behavior. This experimental project will extend our knowledge of the superconducting proximity effect by conducting the first measurements of the thermoelectric and magnetic response of NS structures. In the first part of the project, the energy and length dependence of the electrical conductance of normal wires in contact with a superconductor will be investigated in order to verify fundamental predictions of the theory of NS devices. The second part of the project is devoted to measuring the thermopower of so-called Andreev interferometers, which are loops in which one arm is fabricated from a superconductor and the other from a normal metal. In the last part of the project, the magnetic response of isolated Andreev interferometers will be measured using dc SQUID magnetometers. These last two properties have not been extensively studied, and their measurement should further our understanding of the correlations induced in the normal metal by its proximity to a superconductor. The samples for these experiments will be patterned and fabricated using electron-beam lithography. Their low temperature transport properties will be investigated by linear and nonlinear multiprobe differential resistance measurements as a function of temperature and magnetic field. The low temperature magnetic properties will be measured using ultra-sensitive dc SQUID magnetometers. Post-doctoral associates and graduate students trained on this project will be exposed to a wide variety of experimen tal techniques which will be useful in future careers in either industry or academia. %%% This experimental condensed matter physics project addresses the fabrication and characterization of ultra-small normal metal (N) - superconductors (S) structures. Superconductors have unusual electrical and magnetic properties at low temperatures, the best known being their ability to carry an electrical current without resistance. These properties form the basis for a number of practical devices such as very high field magnets. When a superconductor is placed in good contact with a conventional normal metal such as copper or gold, some of the superconducting properties "leak" a very small distance into the normal metal. With modern lithographic techniques borrowed from the semiconductor industry, it is now possible to probe the properties of normal metals on these very small size scales. The aim of this project is to investigate the electrical, thermoelectric and magnetic properties of such small normal metals placed in close proximity to a superconductor. In the first part of this project, the electrical properties of normal metal wires in proximity to a superconductor will be studied to verify and further our current theoretical understanding of the nature of the superconductivity induced in the normal metal. In the second and third parts of the project, the consequences of this induced superconductivity on the thermoelectric and magnetic properties of the normal metal wires will be explored. These last two properties have not been yet been studied experimentally, and these measurements will help us gain further insight into the interaction between superconductors and normal metals on very small size scales. The samples for these experiments will be fabricated using advanced electron-beam lithography techniques, and measured using sophisticated resistance and magnetic sensors a t temperatures near absolute zero. Post-doctoral associates and graduate students trained on this project will be exposed to a number of experimental techniques which will be useful in future careers in either industry or academia. ***

9801982 Chandrasekhar这个实验凝聚态物理项目致力于正常金属(N)超导体(S)结构的制备和表征，其尺寸与此类材料的基本相干长度相当。对这些纳米结构的电导和其他性质进行了预测和观察，以显示出非经典和令人惊讶的行为。这个实验项目将通过对NS结构的热电和磁响应的首次测量来扩展我们对超导邻近效应的了解。在该项目的第一部分，将研究与超导体接触的正常导线的电导与能量和长度的关系，以验证NS器件理论的基本预测。该项目的第二部分致力于测量所谓的安德列夫干涉仪的热电势，安德列夫干涉仪是一种环路，其中一只手臂由超导体制成，另一只手臂由正常金属制成。在项目的最后部分，将使用DC SQUID磁强计测量孤立的安德列夫干涉仪的磁响应。后两种性质还没有得到广泛的研究，它们的测量应该会进一步加深我们对正常金属与超导体之间的关联的理解。这些实验的样品将使用电子束光刻技术进行图案化和制造。它们的低温输运特性将通过线性和非线性多探头差分电阻测量作为温度和磁场的函数来研究。低温磁性能将使用超灵敏的DC SQUID磁强计进行测量。在这个项目上接受培训的博士后助理和研究生将接触到各种各样的实验技术，这些技术将在未来的行业或学术界的职业生涯中有用。这个实验凝聚态物理项目致力于超小型正常金属(N)-超导体(S)结构的制备和表征。超导体在低温下具有不同寻常的电磁特性，最著名的是它们能够在没有电阻的情况下携带电流。这些特性构成了许多实际设备的基础，例如超高场磁铁。当超导体与铜或金等常规正常金属接触良好时，一些超导性质会在很小的距离内泄漏到正常金属中。借助于借鉴半导体工业的现代光刻技术，现在可以在这些非常小的尺度上探测正常金属的性质。这个项目的目的是研究这些放置在超导体附近的小的正常金属的电、热电和磁性质。在这个项目的第一部分，我们将研究正常金属导线在超导体附近的电学性质，以验证和深化我们目前对正常金属中诱导的超导电性本质的理论理解。在该项目的第二部分和第三部分中，将探讨这种感应超导电性对正常金属导线的热电和磁特性的影响。最后这两个性质还没有被实验研究过，这些测量将帮助我们在很小的尺度上进一步了解超导体和正常金属之间的相互作用。这些实验的样品将使用先进的电子束光刻技术制造，并使用精密的电阻和磁性传感器进行测量，温度接近绝对零度。在这个项目上接受培训的博士后助理和研究生将接触到一些实验技术，这些技术将在未来的行业或学术界的职业生涯中有用。***