Strongly Correlated Fermi Systems

本基金支持凝聚态和材料物理的理论研究。特别是，该研究进一步发展和应用了先进的方法来描述电子强相互作用（相关）的电子材料。在这项资助下开发的方法将得到广泛应用。智力优势：固体中的强相关性驱动了大量新的和不寻常的物理性质，包括复杂的电荷自旋和轨道有序现象，非常规的超导性，超快的非线性光学响应，大热电系数，巨大的体积坍缩，以及许多金属到绝缘体的转变。在广泛的温度和成分范围内，固体的标准模型很难描述强相关材料，它无法描述诸如异常大的金属电阻率和在大频率间隔内的谱权转移等现象。这些材料对凝聚态理论提出了很高的智力挑战，需要一个新的理论框架来解释它们独特的物理性质。需要一种非微扰的方法来从第一性原理计算它们的物理性质，并且必须开发这些复杂系统的简单图像来伴随分析和数值计算。动态平均场理论（DMFT）通过将复杂的多体问题简化为自洽杂质（或杂质簇）模型，为这些有趣的问题提供了一种方法，该模型给出了这些复杂材料的更简单的图像，并允许在标准固体理论不适用的参数体系中计算它们的物理性质。我们的研究将强相关现象的低能量简化图像与模拟真实材料微观复杂性的计算密集型计算联系起来。目标和方法：本基金包括以下项目：_发展复杂相关材料电子结构实际计算的第一性原理方法。这种方法将建立在重整化和DMFT思想的基础上。我们将利用模型哈密顿和第一性原理技术的结合，探索层状钴酸盐的不寻常性质和这类材料中大热电响应的起源。我们将研究相关材料中存在的不寻常电子激发的描述。特别是，我们将研究使用新开发的Cellular DMFT技术在描述铜氧化物和kappa有机盐的模型中接近莫特跃迁时费米表面的破坏。我们将研究接近不同形式的秩序对这一现象的影响。我们还将探讨当近藤相互作用与RKKY交换能相当时，重费米子系统中电子激发性质的演变。更广泛的影响。我们的长期研究目标是开发能够解释并最终预测含有相关电子的固体性质的方法和技术。我们相信理论最终将在实际应用的材料设计中发挥重要作用。我们对材料的理解将为材料的设计提供新的途径，强相关材料将在这一领域发挥重要作用。在开发概念和工具以获得对这一领域的理解的同时，我们也在培养博士后助理、研究生和本科生。这些人正在发展分析和解决复杂问题以及进行分析和数值计算所需的技能，这些技能可以为我们的技术社会做出重要贡献。这项工作的大部分将与欧洲团体合作完成。这将为博士后和学生提供良好的学习经验。

This grant supports theoretical research on condensed matter and materials physics. In particular, the research furthers the development and applications of advanced methods to describe electronic materials in which the electrons are strongly interacting (correlated). The methods developed on this grant will find widespread application.Intellectual Merit: Strong correlations in solids drive a wealth of new and unusual physical properties, ranging from complex charge spin and orbital ordering phenomena, unconventional superconductivity, ultrafast nonlinear optical responses, large thermoelectric coefficients, huge volume collapses, and numerous metal-to-insulator transitions. Over a wide range of temperatures and compositions, strongly correlated materials are poorly described by the standard model of solids, which is unable to describe phenomena such as anomalously large metallic resistivities and transfer of spectral weight over large frequency intervals. These materials pose a high intellectual challenge to condensed matter theory, demanding a new theoretical framework to account for their unique physical properties. A nonperturbative methodology is needed to compute their physical properties from first principles, and simple pictures of these complex systems must be developed to accompany analytic and numerical computations. Dynamical Mean Field Theory (DMFT) provides an approach to these interesting issues by reducing the complex many-body problem to self-consistent impurity (or to a cluster of impurity) models, which give a simpler picture of these complex materials and allow the computation of their physical properties in parameter regimes where the standard theory of solids does not apply. Our research links the low energy simplified pictures of the strong correlation phenomena to the computationally intensive calculations that model the microscopic complexity of real materials.Objective and methods: This grant includes the following projects:_ We will develop a first-principles approach for practical computation of the electronic structure of complex correlated materials. This approach will build on renormalization and DMFT ideas. We will explore the unusual properties of the layered cobaltates and the origin of the large thermoelectric response in this class of materials using a combination of model Hamiltonian and first principles techniques. _ We will investigate the description of the unusual electronic excitations present in correlated materials. In particular, we will study the destruction of the Fermi surface as the Mott transition is approached in models describing copper oxides and kappa organic salts with newly developed Cellular DMFT technique. The influence of proximity to different forms of order on this phenomenon will be investigated. We will also explore the evolution of the nature of the electronic excitations in heavy Fermion systems when the Kondo interaction is comparable to the RKKY exchange energy.Broader Impact. Our long-term research objectives are to develop methods and techniques capable of explaining and ultimately predicting the properties of solids that contain correlated electrons. We believe that theory will ultimately play an important role in the design of materials for practical applications. Our advances in understanding materials will provide new avenues for designing them, and strongly correlated materials will play an important role in this area. While developing concepts and tools to gain understanding in this area, we are at the same time training post-doctoral associates graduate and undergraduate students. These individuals are developing the skills needed to analyze and solve complex problems and perform analytic andnumerical computations, skills that can make important contributions to our technological society. Much of this work will be accomplished in collaboration with European groups. This will provide excellent learning experiences for postdoctoral associates and students.