CAREER: Strange Metal Properties and Superconductvity in Heavy Fermion Materials: Realistic Band Theory Meets Model Hamiltonian Approach

该职业奖支持理论和计算研究和教育，旨在促进对具有强相互作用电子的材料中出现的量子现象的理解。强相关金属的行为不同于普通金属，如铝或铜，因为它们组成的带电可移动粒子不同于普通电子。当电流或热流通过普通金属时，在第一近似上，电子可以看作是独立运动的，彼此之间的相互作用非常弱。然而，当电流通过强相关金属时，电子失去了它们的个性，形成了集体激励。因此，研究人员将这种强烈相关的金属称为“奇怪的金属”。集体行为的一个经典类比是鸟群飞行的复杂模式，尽管由数千只鸟组成，但它们的行为似乎是一个整体。一类令人着迷的奇怪金属被称为“重费米子”物质，在这种物质中，组成粒子之间的相互作用是如此强烈，以至于它们获得了非常重的质量，有时比一个裸电子的质量大几百倍。由于这种重量，许多材料的性能，包括导电性和导热性，都受到深刻影响。不幸的是，使这些材料如此有趣的特征——电子之间的强相互作用——也使它们的研究非常具有挑战性。这项研究活动旨在发展新的、创新的理论和计算方法来研究重费米子材料的电子性质。此外，PI将结合现有的量子化学方法和最先进的计算技术来捕捉这些材料的显著特征，特别是磁性和各种有趣的量子力学特性之间的相互作用，例如材料在不损失任何功率的情况下导电的能力，称为超导性。该奖项将允许PI将教育和推广活动与基础研究结合起来。教育部分将包括参与在职教师的继续教育课程，最终目标是帮助用现代物理内容丰富初中和高中课程，以磁性和超导的概念为中心，这是本研究的核心。该奖项还将支持在凝聚态理论前沿的研究生和博士后研究助理的教育。它将部分支持旨在展示电磁力在现代物理学中的作用的广泛推广工作。它将面向普通公众和学童，目的是普及科学，提高公众对科学重要性的认识。该职业奖支持在重费米子材料中所谓的奇怪金属（非费米液体）行为的理论研究，特别是接近从磁铁到普通金属的量子相变。最近的实验进展已经确定了一些材料，其中的量子临界性不能用已建立的赫兹-米利斯理论来理解。此外，新的量子相经常出现在量子跃迁附近，例如机制尚未完全了解的非常规超导。这些问题将在目前的研究计划中进行研究，其目标有四个方面：(1)利用量子化学和现有最先进的技术相结合来分析重费米子材料中奇怪金属态的性质，以捕获强电子相互作用。(2)开发处理强电子相关性的新方法，特别是在接近量子临界的情况下。PI将开发的一个有希望的方法是使用SU(N) Schwinger玻色子表示局域矩的大N从费米子方法。这种方法已经被证明在单一的近藤杂质中表现良好，最终目标是使其适用于密集的近藤晶格，这描述了重费米子材料的低能部分。(3)研究由此产生的新量子现象，特别是非常规的超导性及其与磁性的相互作用。PI将采用变分克鲁泽近似，它特别适合于研究有序相。将在(2)中发展的大n从费米子方法也将被使用。将各种方法的结果与实验进行比较。(4)在定性上，重费米子系统可以用所谓的Doniach相图来理解，该相图描述了Kondo筛选抑制局域矩之间的磁Ruderman-Kittel-Kasuya-Yosida相互作用。与此同时，人们早就知道磁挫折也会破坏远程磁秩序。最近，包括PI在内的几位研究人员提议将这两种机制结合成一个广义相图，这与最近发现的一些重费米子材料有关。PI将使用多种方法研究磁挫折和近藤效应之间的相互作用，包括前面提到的大n从费米子方法。该奖项将允许PI将教育和推广活动与基础研究结合起来。教育部分将包括参与在职教师的继续教育课程，最终目标是帮助用现代物理内容丰富初中和高中课程，以磁性和超导的概念为中心，这是本研究的核心。该奖项还将支持在凝聚态理论前沿的研究生和博士后研究助理的教育。它将部分支持旨在展示电磁力在现代物理学中的作用的广泛推广工作。这将涉及到普通公众和学童，目的是普及科学，提高公众对科学重要性的认识。

NON-TECHNICAL SUMMARYThis CAREER award supports theoretical and computational research and education, aimed at advancing the understanding of emergent quantum phenomena in materials with strongly interacting electrons. Strongly correlated metals behave differently from ordinary metals such as aluminum or copper because the electrically charged mobile particles of which they consist are unlike ordinary electrons. When an electric current or thermal heat flow travels through an ordinary metal, to a first approximation the electrons can be treated as moving independently and interacting only very weakly with each other. However, when a current travels through a strongly correlated metal, the electrons lose their individuality and form collective excitations. Accordingly, researchers call such strongly correlated metals "strange metals." A classical analogy of a collective behavior is the complex pattern of a flying flock of birds, seemingly behaving as one unit despite comprising thousands of individual birds. A fascinating class of strange metals is harbored by the so-called "heavy fermion" materials, in which the interactions between the constituent particles are so strong that they acquire a very heavy mass, sometimes several hundred times greater than that of a bare electron. As a result of this heaviness, many material properties, including electrical and thermal conductivity, are profoundly affected. Unfortunately, the very feature that makes these materials so interesting - strong interactions between electrons - also makes them very challenging to study. This research activity is aimed at developing new, innovative theoretical and computational methods to study the electronic properties of the heavy fermion materials. In addition, the PI will combine existing methods of quantum chemistry with the state-of-the-art computational techniques to capture the salient features of these materials, in particular the interplay between magnetic and various interesting quantum mechanical properties such as the ability of materials to conduct electricity without any loss of power, called superconductivity.This award will allow the PI to integrate educational and outreach activities with the fundamental research. The educational component will include participation in a continuing education course for in-service teachers, with the ultimate goal of helping enrich the middle- and high-school curricula with modern physics content, centered on the concepts of magnetism and superconductivity that are central to this research. This award will also support the education of a graduate student and a postdoctoral research associate at the frontiers of condensed matter theory. It will partially support a broad outreach effort aimed at showcasing the role of electromagnetic forces in modern physics. It will reach out to the general public and schoolchildren with the goal of popularizing science and increasing public awareness of its importance.TECHNICAL SUMMARYThis CAREER award supports theoretical research in the so-called strange metal (non-Fermi liquid) behavior in heavy fermion materials, in particular close to quantum phase transition from a magnet to an ordinary metal. Recent experimental advances have identified a number of materials in which the quantum criticality cannot be understood in terms of the established Hertz-Millis theory. In addition, new quantum phases often emerge in the vicinity of a quantum transition, such as unconventional superconductivity whose mechanism is not completely understood. These problems will be studied in the present research program, whose objectives are fourfold: (1) To analyze the nature of the strange metal state in heavy fermion materials by using a combination of quantum chemistry and existing state-of-the-art techniques to capture strong electron interactions.(2) To develop novel methods to treat strong electron correlations, in particular in proximity to quantum criticality. One promising approach that the PI will develop is the large-N slave-fermion approach using SU(N) Schwinger boson representation for localized moments. This approach has been demonstrated to perform well for a single Kondo impurity and the ultimate goal is to make it work for a dense Kondo lattice, which describes the low-energy sector of heavy-fermion materials.(3) To address new quantum phenomena emerging from this proximity, in particular the unconventional superconductivity and its interplay with magnetism. The PI will employ the variational cluser approximation, which is particularly well suited to study ordered phases. The large-N slave-fermion approach, to be developed in (2) will also be used. The results of various methodologies will be compared to experiment.(4) Qualitatively, the heavy fermion systems can be understood in terms of the so-called Doniach phase diagram, describing the suppression of magnetic Ruderman-Kittel-Kasuya-Yosida interaction between localized moments by the Kondo screening. At the same time, it has long been known that magnetic frustrations can also destroy long-range magnetic order. Recently, several researchers, including the PI, have proposed to combine these two mechanisms into a generalized phase diagram, pertinent to a number of recently discovered heavy fermion materials. The PI will study the interplay between magnetic frustrations and the Kondo effect using a variety of approaches, including the aforementioned large-N slave-fermion method. This award will allow the PI to integrate educational and outreach activities with the fundamental research. The educational component will include participation in a continuing education course for in-service teachers, with the ultimate goal of helping enrich the middle- and high-school curricula with modern physics content, centered on the concepts of magnetism and superconductivity that are central to this research. This award will also support the education of a graduate student and a postdoctoral research associate at the frontiers of condensed matter theory. It will partially support a broad outreach effort aimed at showcasing the role of electromagnetic forces in modern physics. This will reach out to the general public and schoolchildren with the goal of popularizing science and increasing public awareness of its importance.