U.S.-Federal Republic of Germany Cooperative Research: Microscopic and Phenomenological Theories of Correlated Fermi Systems

该奖项支持教授P. J.赫希菲尔德和K。A.穆塔利布 与佛罗里达大学保持合作研究 与凝聚态物质研究所的Peter Woelfle博士的联系 德国联邦共和国卡尔斯鲁厄大学理论。 他们计划利用超导体来研究超导性和磁性。 单带Hubbard模型，这可能与材料有关 具有高超导转变温度（“高Tc 材料.“）他们将采用两种新的方法，他们最近 开发：1）一个新的功能积分方法，2）一个保存 从玻色子图解展开，研究几个问题 与Hubbard型超导体的可能性有关 系统，费米液体状态的稳定性，在存在的 强相关性，以及无公度反铁- 磁相位 他们还将研究非传统的 超导电性，重点是如何的问题 可以确定非常规序参量的对称性 尤其是电磁探头 虽然负责配对的机制在高 高温超导体即使在两年后仍然神秘 自发现以来，人们进行了大量的研究， 有证据表明，电子相关性，而不是电子-声子 相互作用起着关键作用。 不幸的是， 有足够的系统和受控的方法来处理 有如此强的相关性。 新的方法，如 在这里使用的是必不可少的所有高度相关的研究 费米系统，并应普遍适用于任何类似的 模型，包括适用于高Tc材料的模型。 这些 新的方法起源于广泛的合作， 当Woelfle博士花了几年时间在 佛罗里达大学。 继续互动应该证明 是非常有成效和互利的。

This award supports Professors P. J. Hirschfeld and K. A. Muttalib of the University of Florida to maintain collaborative research links with Dr. Peter Woelfle of the Institute for Condensed Matter Theory of the University of Karlsruhe, Federal Republic of Germany. They plan to investigate superconductivity and magnetism using the single band Hubbard model, which is possibly relevant to materials with high superconducting transition temperatures ("high-Tc materials.") They will apply two new methods that they recently developed: 1) a new functional integral approach, and 2) a conserving slave boson diagrammatic expansion, to study several questions related to the possibility of superconductivity in Hubbard-like systems, the stability of the Fermi liquid state in the presence of strong correlations, and the stability of incommensurate antiferro- magnetic phases. They will also study models of unconventional superconductivity, with an emphasis on the question of how the symmetry of an unconventional order parameter can be determined with external probes, particularly electromagnetic ones. Although the mechanisms responsible for pairing in the high temperature superconductors remain mysterious even after two years of intense research since its discovery, there is accumulating evidence that electronic correlations, rather than electron-phonon interaction play a crucial role. Unfortunately, there is no adequate systematic and controlled method available for dealing with such strongly correlated systems. New methods such as those being used here are essential for the study of all highly correlated Fermi systems, and should be generally applicable to any similar model, including that appropriate for the high-Tc materials. These novel methods originated as a result of extensive collaboration among these scientists when Dr. Woelfle spent several years at the University of Florida. Continuing the interaction should prove to be very productive and mutually beneficial.