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

强相关电子系统中的无序和非均匀相的出现

• 批准号: 2231821
• 负责人: Peter Hirschfeld
• 金额: $ 40万
• 依托单位: University of Florida
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-12-15 至 2026-11-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2231821&HistoricalAwards=false
• 关键词: Disorder; Emergence; Inhomogeneous; Phases; Strongly

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.

该奖项支持理论和计算研究和教育，旨在促进对导电但含有电子的材料的理解，这些材料相互施加强大的力，导致电子物质的新状态。这些量子材料具有新颖的特性。PI将使用模型计算铜酸盐和铁基超导体等材料中的电子，以及其他材料，研究几个具有挑战性的问题，以更广泛地了解这些材料是如何工作的。他还将与当地一家科学博物馆合作，为公众准备超导和磁性的展览，并组织旨在鼓励年轻女学生和研究人员考虑从事物理学事业的活动。超导是金属中许多电子的量子态，其特征是失去所有电阻，从而导致所有能量的耗散。PI将探索超导体的基本物理与物质的其他相之间的相互作用，包括磁性相，当超导性被抑制时，磁性相往往会形成。此外，他将探索化学杂质的影响，晶体中的一个原子被不同的元素取代，以及晶体或薄膜生长时经常出现的其他缺陷的影响。特别地，这些杂质如何决定所实现的阶段将被处理。例如，次级相的“岛”或液滴可能出现在超导体的主导相中。因此，PI将探索杂质和其他实际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。当扫描材料表面时，该技术通过对微小的尖锐金属尖端施加电压来显示材料量子态的原子分辨率图像-有效地拍摄量子态的原子尺度“照片”。从这些实验的理论计算和数据分析中获得的信息可能为超导性和其他量子态的相互作用提供关键的见解，包括磁性和一种新的电子“电子向列”状态，这是一种量子力学模拟状态，使液晶显示成为可能。这些研究的一个结果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导致新的特性，这些特性可以用于新的设备和技术，例如在高度相关金属的竞争相之间的边界附近具有异常灵敏度的传感器。该奖项支持理论和计算研究和教育，以解决长期存在的基本问题，涉及相关电子系统中淬火无序和各种类型的竞争紧急秩序的相互作用。要研究的材料包括铜基和铁基超导体，以及其他显示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性质，在某些情况下，通过基于密度泛函理论的电子结构计算，适当地包含相关性。主要有三个项目：1。无序对过量掺杂铜酸盐的影响。PI将对可以掺杂超过最佳掺杂的铜材料进行一系列研究，以说明面外掺杂的散射的意想不到的影响，并测试使用DFT的万尼尔函数衍生散射势开发的杂质散射的材料特异性理论。PI和他的团队将开发材料特定的杂质电位，以了解正常和超导状态的传输，其中杂质的正向散射可能很重要，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和间隙闭合的T之间也存在很大的差异。该团队将尝试计算有多少间隙填充现象是由于在过渡附近的无序诱导的非均匀性，也就是说，当系统分解成弱邻近耦合的良好超导体的小岛屿时。这些现象学研究将辅以自旋涨落理论的微观研究，其中本征对相互作用的掺杂依赖是hubard型的，并被无序修饰，以研究Tc在过掺杂侧的消失。电荷和对密度波的STM。许多关于竞争秩序和非均匀性的物理信息来自高质量表面的扫描隧道显微镜和光谱学；然而，解释这些数据的理论还只是非常原始的形式。PI将使用从头计算的微观万尼尔函数来构建超导和金属状态下的局部格林函数，以与电荷和对密度波的实验进行比较，计算实际进行测量的样品表面以上状态的局部密度。特别是，PI将发展扫描约瑟夫森光谱学理论，使用万尼尔函数连续表示计算局部临界电流，在相干和扩散体制下，与目前正在进行的约瑟夫森STM实验进行比较。理解相关电子系统的特性和无序的影响可能会导致新的材料特性，这些特性可以用于新的设备和技术，通过在高度相关电子系统中发生的竞争相之间的近跃迁操作获得不同寻常的灵敏度。弹性散射下二碲化铀的热输运和穿透深度。自旋三重态重费米子超导体二碲化铀仍然很神秘，超导间隙的结构也不为人所知。热导率实验提示点节点，而穿透深度实验提示节点可能远离高对称点分布。PI将发展两种三重态实验探测器的理论来解决这些问题，包括提出的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导电和超导的新展览，组织佛罗里达大学活动以支持联合国妇女和女童参与科学日，以及编写和发表公开讲座。为计算自旋涨落配对而开发的软件，以及非常规超导体中的万尼尔函数数据库，将通过PI的网站和GitHub提供。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。