Electrodynamics of Superconductors

该项目旨在研究新型超导材料（如高温超导体和硼碳化物超导体）在微波频率下对电磁波的响应。实验将使用某些独特的设备来研究各种条件和材料下的微波响应。经过适当的分析，这种响应将产生关于这些材料中电子成对状态和超导涡旋运动的重要信息。除了对高温超导体和硼碳化物超导体的理解做出基础贡献外，这项工作还将对微波应用产生重要影响。了解纯系统的内在特性，纯度的影响，将为提高微波器件的损耗能力提供线索。非线性效应的研究对于提高微波器件的高功率性能至关重要，是目前制约高温超导材料在这一领域成功应用的一个严重问题。高低温超导体的电磁响应将使用独特的实验能力进行研究，涵盖广泛的频率范围（直流到50千兆赫），温度范围（2到350开尔文）和磁场范围（0到7特斯拉）。该计划将解决当前的关键问题，如序参数对称、态准粒子密度、磁场在迈斯纳态和混合态中的依赖效应、c轴传输（包括相干/非相干准粒子隧穿）和本征约瑟夫森结的可能性。高温超导体的一个显著特征是在中等微波功率和场幅下具有明显的非线性响应。从高频磁通穿透的时空动态角度理解这种非线性将是本项目的另一个主题。实验将在频域和时域进行非线性阻抗，混合ac和谐波/互调响应，并将在最近出现的临界状态模型框架内进行分析。＊＊＊

9623720 Sridhar This project seeks to study the response to electromagnetic waves at microwave frequencies, of new superconducting materials, such as high temperature superconductors and borocarbide superconductors. Experiments will be carried out using certain unique facilities to study microwave response under a variety of conditions and materials. This response, when suitably analyzed, will yield important information about the paired state of electrons and the motion of superconducting vortices in these materials. In addition to making fundamental contributions to the understanding of high temperature and borocarbide superconductors, this work will also have important impact on microwave applications. An understanding of the intrinsic properties of the pure systems, the the influence of purities, will provide clues to improving the loss capabilities of microwave devices. The studies of non-linear effects will be crucial to improving the high power performance of microwave devices, currently a serious limitation to the successful application of the high temperature superconducting materials in this arena. %%% The electromagnetic response of high and low temperature superconductors will be investigated using a unique experimental capability, covering a wide range of frequencies (dc to fifty gigahertz), temperature (2 to 350 Kelvin) and magnetic field (0 to 7 Tesla). The program will address key current issues, such as order parameter symmetry, quasiparticle density of states, depairing effects of a magnetic field in the Meissner and mixed states, c-axis transport including coherent/incoherent quasiparticle tunneling and possibility of intrinsic Josephson junctions. A notable feature of the high temperature superconductors is their pronounced non-linear response at moderate microwave powers and field amplitudes. An understanding of this non-linearity in terms of th e spatio-temporal dynamics of flux penetration at high frequencies will be another theme of this project. Experiments will be carried out on the non-linear impedance, mixed acdc and harmonic/intermodulation response, in both the frequency-domain and time-domain, and will be analyzed in the framework of critical state models which can have recently emerged. ***