Transport and Magnetic Properties of NS Structures

这个实验凝聚态物理项目解决了正常金属(N) -超导体(S)结构的制造和表征，其尺寸与此类材料的基本相干长度相当。这些纳米结构的电导率和其他特性被预测和观察到，显示出非经典和令人惊讶的行为。该实验项目将通过对NS结构的热电和磁响应进行首次测量，扩展我们对超导邻近效应的认识。在项目的第一部分，将研究与超导体接触的正常导线的电导率的能量和长度依赖关系，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Andreev干涉仪的热功率，这种干涉仪是一种环路，其中一条臂由超导体制成，另一条臂由普通金属制成。在项目的最后一部分，将使用直流SQUID磁力计测量孤立安德烈夫干涉仪的磁响应。后两种性质还没有得到广泛的研究，它们的测量应该进一步加深我们对正常金属中由于接近超导体而引起的相关性的理解。用于这些实验的样品将使用电子束光刻进行图案化和制造。通过线性和非线性的多探头差分电阻测量来研究它们的低温输运特性作为温度和磁场的函数。低温磁性能将使用超灵敏直流SQUID磁力计进行测量。在这个项目中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，这些技术将对未来在工业界或学术界的职业生涯有用。这个实验凝聚态物理项目解决了超小型正常金属(N) -超导体(S)结构的制造和表征。超导体在低温下具有不同寻常的电和磁特性，最著名的是它们能够无电阻地传输电流。这些特性构成了许多实际设备的基础，例如非常高的磁场磁铁。当超导体与传统的普通金属（如铜或金）接触良好时，一些超导特性会“泄漏”到普通金属中非常小的距离。借助从半导体工业借鉴的现代光刻技术，现在可以在这些非常小的尺寸尺度上探测普通金属的性质。这个项目的目的是研究放置在超导体附近的这种小的正常金属的电学、热电和磁性。在这个项目的第一部分，将研究接近超导体的普通金属线的电学特性，以验证和进一步我们目前对普通金属中诱导的超导性质的理论理解。在项目的第二和第三部分，将探讨这种诱导超导性对普通金属线的热电和磁性能的影响。最后两个性质还没有经过实验研究，这些测量将帮助我们进一步了解超导体和普通金属在非常小尺寸尺度上的相互作用。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传感器在接近绝对零度的温度下进行测量。在这个项目中接受培训的博士后助理和研究生将接触到许多实验技术，这些技术将对未来在工业界或学术界的职业生涯有用。＊＊＊

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. ***