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

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学院的Yuri Barash合作。该合作将研究一系列与d波超导体表面特性相关的问题，这些问题与铜和其他具有非常规超导性的新材料有关。科学问题包括在相关（正常和超导）系统中建立晶界模型，以预测输运性质和提取有关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，其他有序态的能量相对较低，并且可能在d波有序被抑制时表现出来，例如在表面、晶界或无序区域。最近在BSCCO-2212体系中观察到纳米级电子结构的非均匀性，并且有证据表明这种紊乱不仅是内在的，而且可能为高tc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级结构的起源。更广泛的影响：如果能解决晶界问题，将对超导微波和电力应用产生巨大的实际影响。目前，限制电线和胶带临界电流Jc的影响似乎是所有样品中晶界的存在。目前还没有从基本层面上理解为什么晶粒之间的取向角错误会导致Jc的指数抑制，但很明显，序参量的d波对称性是一个关键因素。众所周知，简单的现象学图像是失败的，如果提出的研究可以提供答案，这个重要的应用障碍将被克服。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的培训。从某种意义上说，对更广泛的社区的好处将会增加，因为讨论的许多想法也与几类正在受到严密科学审查的新型超导体有关，包括有机超导体、钌酸盐、重费米子和硼碳化物。调查结果将通过出版物、PI网站以及佛罗里达大学和其他地方的研讨会进行传播。

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.