US-Germany Cooperative Research: Theory of Grain Boundaries and Surfaces of High Temperature Superconductors

0340536该奖项支持Peter Hirschfeld和佛罗里达大学的学生与德国奥格斯堡大学物理系的Thilo Kopp和俄罗斯莫斯科物理与技术研究所的Yuri Barash合作。这项合作将研究与铜酸盐相关的d波超导体表面性质的一系列问题，以及其他显示非传统超导电性的新材料。这些科学问题包括对相关(正常和超导)系统中的晶界进行建模，以预测输运性质，并提取关于非常规超导和磁序参数对称性的信息。近年来，除了d波超导性之外的其他有序态的能量相对较低，并且当d波有序被抑制时，例如，在表面、晶界或无序区，它们可能会表现出来。最近在BSCCO-2212体系中观察到了电子结构的纳米尺度不均匀，有证据表明这种无序可能不仅是本征的，而且可能为高T_c超导的起源提供重要线索。表面和颗粒的现象学研究将有助于理解这些纳米结构的起源。该提议的广泛影响如果晶界问题能够得到解决，将对超导微波和功率应用具有巨大的实际意义。目前，限制线和带材的临界电流Jc的效应似乎是所有样品中都存在晶界。目前还不能从根本上理解为什么JC随晶间错向角呈指数抑制，但很明显有序参数的d波对称性是一个关键因素。简单的现象学图像是众所周知的失败的，如果拟议的调查能够提供答案，这一应用的重要障碍将被克服。该提案的更广泛影响还包括对美国研究生的教育好处，他们将在国际环境中接受与这些问题有关的方法培训。更广泛的社区将受益，因为许多讨论的想法也与严格科学审查下的几类新型超导体有关，包括有机超导体、Ruthenate、重费米子和碳化硼。结果将通过出版物、国际和平协会的网站以及在佛罗里达大学和其他地方举行的研讨会来传播。

0340536HirschfeldThis award supports Peter Hirschfeld and students from the University Florida in a collaboration with Thilo Kopp of the Department of Physics at the University of Augsburg, Germany and Yuri Barash of the Moscow Institute of Physics and Technology in Russia. The collaboration will investigate a series of problems related to surface properties of d-wave superconductors relevant to cuprate and other novel materials displaying unconventional superconductivity. The scientific problems include the modeling of grain boundaries in correlated (normal and superconducting) systems to predict transport properties and extract information regarding unconventional superconducting and magnetic order parameter symmetry. In recent years it has become clear that other ordered states besides d-wave superconductivity are relatively low in energy, and may manifest themselves when the d-wave order is suppressed, e.g., at surfaces, grain boundaries, or regions of disorder. Nanoscale inhomogeneity in electronic structure has recently been observed in the BSCCO-2212 system, and there is some evidence that this disorder may not only be intrinsic, but may provide an important clue to the origin of high-Tc superconductivity. Phenomenological studies of surfaces and grains will aid in understanding the origin of these nanoscale structures.Broader impact of the proposalThere are enormous practical implications for superconducting microwave and power applications if the grain boundary problem can be solved. At present the effect limiting the critical current Jc in wires and tapes appears to be the presence of grain boundaries in all samples. It is not currently understood at a fundamental level why there is an exponential suppression of Jc with the misorientation angle between grains, but it is clear that the d-wave symmetry of the order parameter is a crucial factor. Simple phenomenological pictures are known to fail, and if the proposed investigations can provide an answer, this important obstacle to applications will be overcome. The broader impact of the proposal also includes the educational benefits to the US graduate students, who will be trained in an international setting in methods pertaining to these problems. Benefits to a wider community will accrue in the sense that many of the ideas discussed also pertain to several classes of novel superconductors under intense scientific scrutiny, including the organic superconductors, ruthenates, heavy fermions and borocarbides. Results will be disseminated through publications, the PI's web site, and seminars at the University of Florida and elsewhere.