Disorder and the Emergence of Inhomogeneous Phases in Strongly Correlated Electron Systems

非技术摘要该奖项支持理论和计算研究及教育，旨在促进对导电材料的理解，但含有电子的材料相互施加强大的作用力，从而导致电子物质的新状态。这些量子材料具有新颖的特性。 PI 将使用铜酸盐和铁基超导体等材料类别中的电子模型计算来研究几个具有挑战性的问题，以更广泛地了解这些材料的工作原理。他还将与当地的一家科学博物馆合作，为公众准备有关超导和磁性的展览，并组织旨在鼓励年轻女学生和研究人员考虑从事物理学职业的活动。超导是金属中许多电子的量子态，其特征是失去所有电阻，从而失去所有能量。 PI 将探索超导体的基础物理与物质的其他相（包括磁性相）之间的相互作用，磁性相是在超导性受到抑制时形成的。此外，他还将探索化学杂质的影响（晶体中的原子被不同元素取代），以及晶体或薄膜生长时始终存在的其他缺陷的影响。特别是，这些杂质如何决定所实现的相将得到解决。 例如，第二相的“岛”或液滴可能出现在超导体的主相中。因此，PI 将探索杂质和其他现实缺陷对这些超导材料性能影响的模型。 PI 将特别关注如何解释扫描隧道光谱实验结果的理论。该技术通过在微小的锋利金属尖端上扫描材料表面时施加电压来显示材料量子态的原子分辨率图像，从而有效地拍摄量子态的原子级“照片”。从理论计算和对这些实验数据的分析中获得的信息可以为超导性和其他量子态之间的相互作用提供关键见解，包括磁性和一种新颖的电子“电子向列”态，这是使液晶显示成为可能的状态的量子力学模拟。 这些研究的结果之一可能是更深入地了解高温超导的本质以及如何进一步优化它，这可能具有技术意义。 了解这些量子材料的特性和无序的影响也可能带来可用于新设备和技术的新颖特性，例如在高度相关金属的竞争相边界附近运行的具有异常灵敏度的传感器。技术摘要该奖项支持理论和计算研究和教育，以解决涉及相关电子系统中猝灭无序和各种类型的竞争性涌现秩序相互作用的长期存在的基本问题。要研究的材料包括铜酸盐和铁基超导体，以及其他表现出竞争顺序的量子材料。 PI 将通过仔细分析晶格上相互作用电子的简化模型的行为来研究电子系统的特性，在某些情况下通过基于密度泛函理论的电子结构计算以及适当包含的相关性来提供信息。主要项目有三个： 1． 无序对过量掺杂铜酸盐的影响。 PI将对可以远远超过最佳掺杂的铜酸盐材料进行一系列研究，以说明面外掺杂剂散射的意外影响，并测试使用DFT的Wannier函数导出的散射势开发的材料特定的杂质散射理论。 PI 和他的团队将开发材料特定的杂质势，以了解正常和超导态输运，其中杂质的前向散射可能很重要，特别是在电阻率测量中观察到的角度相关的弹性平均自由程以及太赫兹电导率。 其中一些工作将与西蒙弗雷泽大学的一个小组合作完成。 即使在过掺杂的铜酸盐中，电阻 Tc 和间隙闭合处的 T 之间也存在很大差异。 该团队将尝试计算有多少间隙填充现象是由于过渡附近无序引起的不均匀性造成的，也就是说，当系统分解成弱邻近耦合的良好超导体小岛时。 这些现象学研究将辅以自旋涨落理论的微观研究，其中本征配对相互作用的掺杂依赖性是哈伯德型并被无序修正，以研究过掺杂侧Tc的消失。2．电荷和电子对密度波的 STM。许多关于竞争有序和不均匀性的物理信息都来自于高质量表面上的扫描隧道显微镜和光谱学；然而解释这些数据的理论仅以非常原始的形式存在。 PI 将使用从头计算的微观 Wannier 函数来构建超导态和金属态的局部格林函数，与电荷和对密度波的实验进行比较，计算实际执行测量的样品表面上方的局部态密度。 特别是，PI 将开发扫描约瑟夫森光谱理论，以使用 Wannier 函数连续体表示计算相干和扩散状态下的局部临界电流，以与当前正在进行的约瑟夫森 STM 实验进行比较。 了解相关电子系统的特性和无序的影响可能会产生可用于新设备和技术的新颖材料特性，通过在高度相关电子系统中发生的竞争相之间的过渡附近进行操作来获得异常的灵敏度。3。 具有弹性散射的二碲化铀的热传输和穿透深度。自旋三重态重费米子超导体二碲化铀仍然相当神秘，超导能隙的结构尚不清楚。 热导率实验表明点节点，而穿透深度实验表明节点可能分布在远离高对称点的位置。 PI 将开发三重态实验探针的理论来解决这些问题，包括用于解释克尔效应和时间反转对称性破缺的μ子自旋共振指示的非酉探针理论。 他将进一步研究紊乱在产生这些信号中的作用。 该奖项还支持外展活动，包括：为最近开放的凯德创新博物馆设计一个关于电导和超导的新展览，组织佛罗里达州活动以支持联合国妇女和女童科学日，以及制定和举办公共讲座。为计算自旋波动配对而开发的软件以及非常规超导体中 Wannier 函数的数据库将通过 PI 的网站和 GitHub 提供。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

NONTECHNICAL SUMMARYThis award supports theoretical and computational research and education designed to advance understanding of materials that conduct electricity but contain electrons that apply strong forces on each other which led to new states of electronic matter. These quantum materials have novel properties. The PI will use model calculations for electrons in materials classes known as cuprates and iron-based superconductors, as well as others, to study several challenging problems directed towards a broader understanding of how these materials work. He will also work with a local science museum to prepare exhibits on superconductivity and magnetism for the public, and organize events designed to encourage young women students and researchers to consider a career in physics.Superconductivity is the quantum state of many electrons in a metal that is characterized by the loss of all electrical resistance and consequently of all dissipation of energy. The PI will explore the interplay between the fundamental physics of superconductors and other phases of matter, including magnetic ones, which tend to form when superconductivity is suppressed. In addition, he will explore the effect of chemical impurities, where an atom in a crystal is replaced by a different element, as well as effects of other defects always present when crystals or films are grown. In particular, how these impurities determine the phases that are realized will be addressed. For example, “islands” or droplets of a secondary phase may appear in the dominant phase of a superconductor. Thus, the PI will explore models of the effect of impurities and other real-life defects on the properties of these superconducting materials. The PI will focus especially on the theory of how to interpret results from scanning tunneling spectroscopy experiments. This technique reveals atomic-resolution images of the quantum states of a material by applying a voltage to a tiny sharp metal tip as it is scanned over the material's surface - effectively taking an atomic-scale “photograph” of the quantum state. Information obtained from theoretical calculations and the analysis of data from these experiments may provide key insights into the interplay of superconductivity and other quantum states including magnetism and a novel “electronic nematic” state of electrons that is a quantum mechanical analog of states that make liquid crystal displays possible. One consequence of these investigations may be a deeper insight into the nature of high temperature superconductivity and how it can be further optimized, which could have technological implications. Understanding the properties of these quantum materials and the influence of disorder may also lead to novel properties that can be utilized in new devices and technologies, such as sensors with unusual sensitivity operating near boundaries among competing phases in highly correlated metals.TECHNICAL SUMMARYThis award supports theoretical and computational research and education to address long-standing fundamental problems involving the interplay of quenched disorder and various types of competing emergent order in correlated electron systems. The materials to be investigated include cuprate and iron-based superconductors, as well as other quantum materials displaying competing orders. The PI will study properties of electronic systems through a careful analysis of the behavior of simplified models of interacting electrons on the lattice, informed in some cases by density functional theory-based electronic structure calculations with appropriate inclusion of correlations. There are three main projects:1. Effects of disorder on overdoped cuprates. The PI will perform a series of investigations on the cuprate materials that can be doped well past optimal doping, to illustrate the unexpected effects of scattering from out-of-plane dopants, and test the materials-specific theory of impurity scattering developed using Wannier function-derived scattering potentials from DFT. The PI and his group will develop materials-specific impurity potentials to understand normal- and superconducting-state transport where forward scattering from impurities can be important, in particular the angle-dependent elastic mean free path observed in resistivity measurements, as well as Terahertz conductivity. Some of this work will be done in collaboration with a group at Simon Fraser University. Even in the overdoped cuprates, there is a substantial discrepancy between the resistive Tc and the T where the gap closes. The team will try to calculate how much of the gap filling phenomenon is due to disorder-induced inhomogeneity near the transition, that is, when the system breaks up into small islands of good superconductor that are weakly proximity coupled. These phenomenological studies will be supplemented by microscopic studies of spin fluctuation theory, where the doping dependence of the intrinsic pairing interaction is Hubbard-type and modified by disorder, to study the disappearance of Tc on the overdoped side.2. STM of charge and pair density waves. Much of the physical information available on competing order and inhomogeneity arises from scanning tunneling microscopy and spectroscopy on high quality surfaces; yet the theory to interpret such data is available only in very primitive form. The PI will use microscopic Wannier functions from ab initio calculations to construct local Green's functions in both superconducting and metallic states to compare with experiments on charge and pair density waves, calculating the local density of states above the sample surface where measurements are actually performed. In particular, the PI will develop the theory of scanning Josephson spectroscopy to calculate the local critical current using the Wannier function continuum representation, in both the coherent and diffusive regimes to compare with Josephson STM experiments currently being performed. Understanding the properties of correlated electron systems and the influence of disorder may lead to novel materials properties that can be utilized in new devices and technologies, obtaining unusual sensitivity by operating near transitions between competing phases that occur in highly correlated electron systems.3. Thermal transport and penetration depth in uranium ditelluride with elastic scattering. The spin-triplet heavy fermion superconductor uranium ditelluride is still quite mysterious and the structure of the superconducting gaps are unknown. Thermal conductivity experiments suggest point nodes, while penetration depth experiments imply that the nodes may be distributed away from high symmetry points. The PI will develop the theory of both experimental probes for triplet states to settle these issues, including nonunitary ones proposed to explain Kerr effect and muon spin resonance indications of time reversal symmetry breaking. He will further investigate the role of disorder in producing these signals. This award also supports outreach activities including: designing a new exhibit on electrical conduction and superconductivity for the recently opened Cade Museum for Innovation, organizing U. Florida Activities in support of United Nations Women and Girls in Science Day, and developing and delivering public lectures. Software developed for the calculation of spin fluctuation pairing, and a database for Wannier functions in unconventional superconductors, will be made available through the PI's website and GitHub.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.