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Disorder and quantum criticality in itinerant antiferromagnets

流动反铁磁体中的无序和量子临界性

基本信息

批准号：
225437397
负责人：
Professor Dr. Jörg Schmalian
金额：
--
依托单位：
Institut für Theorie der Kondensierten Materie (TKM)
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2013
资助国家：
德国
起止时间：
2012-12-31 至 2015-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/225437397?language=en
关键词：
Disorder quantum criticality itinerant antiferromagnets

项目摘要

The overall goal is to develop a theory for dynamic excitations and transport near a quantum critical point that takes into account critical fluctuations of all soft modes and disorder due to impurities and imperfections. The recently discovered iron-based high-temperature superconductors as well as investigations of inter-metallic heavy-electron systems and transition-metal oxides demonstrate the need to establish a theoretical framework that accounts for disorder in itinerant antiferromagnets close to criticality. In these systems it is important to analyze simultaneously the impact of disorder on the collective order-parameter degrees of freedom and on the electrons near the Fermi energy. Metals, being governed by gapless electronic excitations, give rise to new critical behavior compared to insulating quantum magnets. In addition to the formal development of a new theoretical framework, our project will be concerned with a detailed comparison with experiments in the mentioned materials. In the limit of vanishing disorder the theory should recover the results obtained from the analysis of fluctuating spin density waves. In the limit of vanishing electron-electron interactions the theory will recover the known behavior of disordered electrons, including weak and strong localization. To develop such a theory is important for a number of reasons: i) it enables us to judge whether some or all of the observations that puzzle the community can be rationalized as being due to the subtle interplay of criticality and disorder, ii) experiments in some systems seem to agree with the conventional theory and our work will make clear predictions with regards to disorder induced novel physics, and iii) the theory that we propose to develop promises to constitute novel critical behavior.We plan to formulate a well-controlled theory to make robust and reliable predictions for thermodynamic, spectroscopic and transport properties of metals near antiferromagnetic quantum phase transitions. We will then develop a controlled calculation where critical fluctuations and disorder are treated on the same footing. The small parameter of the theory is 1/N, where N is the number of fermion flavors (bands). This expansion allows the investigation of the limit of strong disorder and large spin-electron coupling. It was successfully used to solve disordered problems without interactions and includes the physics of localization in strongly disordered or two dimensional systems. It was also used in clean quantum critical systems, where it leads to non-Fermi liquid behavior. We will also address the role of statistically rare regions and droplets that lead to quantum Griffith behavior, activated scaling and smearing of the phase transition.

总体目标是发展一个理论，考虑到所有软模式和无序由于杂质和缺陷的临界波动的量子临界点附近的动态激发和运输。最近发现的铁基高温超导体以及对金属间重电子系统和过渡金属氧化物的研究表明，需要建立一个理论框架，解释接近临界的巡游反铁磁体中的无序。在这些系统中，重要的是要同时分析无序对集体序参数自由度和费米能附近的电子的影响。与绝缘量子磁体相比，金属受无隙电子激发的支配，产生了新的临界行为。除了正式开发新的理论框架外，我们的项目还将关注与上述材料中实验的详细比较。在无序消失的极限下，理论应该恢复从自旋密度波动波的分析中得到的结果。在电子-电子相互作用消失的极限下，该理论将恢复无序电子的已知行为，包括弱定域和强定域。发展这样一个理论是重要的，原因有几个：i）它使我们能够判断是否一些或所有的观察，困惑社会可以合理化，因为是由于微妙的相互作用的临界性和无序，ii）在一些系统中的实验似乎同意与传统的理论和我们的工作将作出明确的预测，关于无序诱导新的物理学，我们提出的理论有望构成新的临界行为，我们计划制定一个良好的控制理论，对反铁磁量子相变附近的金属的热力学，光谱和输运性质进行稳健和可靠的预测。然后，我们将发展一种受控计算，在这种计算中，临界涨落和无序被同等对待。理论的小参数是1/N，其中N是费米子味（带）的数量。这种扩展允许调查的限制强无序和大自旋电子耦合。它被成功地用于解决没有相互作用的无序问题，包括在强无序或二维系统中的物理定位。它也被用于清洁量子临界系统，在那里它导致非费米液体行为。我们还将讨论统计上罕见的区域和液滴的作用，导致量子格里菲斯行为，激活缩放和涂抹的相变。