CAREER: Generic Phase Diagram of the Mixed State of Type IISuperconductors

本项目主要研究II型超导体中磁通穿透的相图。PI对铜超导体中通量晶格所经历的固-液转变的发现刺激了对这一相图的II型超导体的更广泛的研究。特别令人感兴趣的是各向异性、无序和热波动对产生新观察到的旋涡液体和II型超导体的相关状态的影响。实验将测量由磁通运动产生的线性和非线性电阻率与温度和磁场的关系。此外，临界电流和能量势垒（活化能）将被测量。磁通流电压的实验测量将涵盖非常广泛的电压动态范围：使用定制的基于squid的电压表从亚皮伏到纳伏范围，使用最先进的商用电压表从纳伏到毫伏范围。要研究的材料包括铜和传统的层状超导体。拟议中的研究将被纳入一项教育计划，以帮助提高学生的学习并培养未来的科学家，包括代表性不足的少数群体的成员。这个CAREER基金项目涉及磁场与超导态相互作用的基础实验研究。研究的重点是II型超导体，II型超导体比I型超导体对磁场的容忍度更高，因为磁场可以以量子化磁通线或涡流的形式穿透II型超导体，而不一定破坏零电阻状态。在II型超导体中，当电流密度对磁通线施加足够强的力使其移动时，就会产生电阻，从而产生热效应。因此，这一研究领域与超导体在涉及大电流和高磁场的应用中的电流处理能力有关，例如电机或发电机中的电力电缆和绕组。在这方面，近年来在高转变温度铜超导体中发现了一种新的现象，即量子化磁通线的熔化或液体运动，这种现象在载流电缆中特别有应用前景。因此，在这个项目中进行的基础研究有望在长期内为改进电力技术作出贡献。这项研究将被纳入一项教育计划，以帮助提高学生的学习能力并培养未来的科学家，包括代表性不足的少数群体的成员。＊＊＊

w:\awards\awards96\num.doc 9702535 Safar This experimental CAREER grant project focuses on the phase diagram describing the flux penetration in Type II superconductors. The discovery by the PI of the solid-liquid transition undergone by the flux lattice in the cuprate superconductors spurs investigation more generally among Type II superconductors of this phase diagram. Of particular interest are the effects that anisotropy, disorder and thermal fluctuations have on creating the newly observed vortex liquid and related states of the Type II superconductor. The experiments will measure the temperature and magnetic field dependencies of the linear and nonlinear resistivities which arise by flux motion. In addition, the critical currents, and energy barriers (activation energies) will be measured. The experimental measurement of flux- flow voltages will cover a very broad voltage dynamic range: sub- picovolt to nanovolt range using a custom-built SQUID-based voltmeter, and from nano to millivolts using state of the art commercial voltmeters. The materials to be studied include both cuprate and conventional layered superconductors. The proposed research will be integrated into an education plan to help enhance student learning and to train future scientists, including members of under-represented minority groups. %%% This CAREER grant project involves fundamental experimental research on the interaction of magnetic fields with the superconducting state. It is focused on the Type II superconductors, which are more tolerant of magnetic field than Type I superconductors, in that magnetic field can penetrate the Type II superconductor in the the form of quantized flux lines or vortices, without necessarily destroying the zero resistance state. Electrical resistance, and therefore heating effects, occur in Type II superconductors when the current density, exerts a sufficiently strong force on the flux lines to cause them to move. This field of research therefore is relevant to the current handling capacity of superconductors in applications involving high currents and high magnetic fields, such as electric power cables and windings in motors or generators. A new phenomenon in this connection, melting or liquid-like motion of the quantized flux lines, has been discovered in the past few years in the high transition temperature cuprate superconductors, which are particularly promising for applications in current carrying cables. The fundamental research carried out in this project therefore is expected to contribute in the long term to an improved electric power technology. The research will be integrated into an education plan to help enhance students learning and to train future scientists, including members of under-represented minority groups. ***