Density Response and Electron Pairing

该奖项支持研究和教育，以提高我们对电子如何响应其环境变化及其形成配对而不是保持相对独立的趋势之间关系的理解。固体中的电子配对是固体中几种最有趣和最有用的性质的根源，超导性和非均匀磁性是两个重要的例子。2016年在三硫化氢中发现临界起始温度（Tc）高于200 K（-85 F）的超导性，建立了Tc的新纪录，促进富氢材料成为这一研究领域的新前沿。 高温超导性的这场革命是以需要一个封闭的压力单元来提供诱导超导性的200万个大气压为代价的。为了取得进展，如果要发现更高Tc或更低压力的例子，理论和模拟必须发挥更大的作用。 现有的模拟几个候选人的质子（氢原子核）揭示了需要了解在一个基本的水平上的金属传导电子与振动的质子（氢原子核）的相互作用。 该项目将利用这个材料平台来解决一个基本问题，即为什么有些超导体是壮观的超导体，而其他看似相似的超导体却不是。类似的模拟将被应用于其他特殊的超导体（即单层硒化铁），其中相关类型的配对是促进超导临界温度令人印象深刻的增强的最佳候选者。首席研究员将扩展和应用相关理论，并编写计算机代码，用于研究这一问题所需的计算。通过进入技术领域，超导性正在实现更广泛的影响，而不仅仅是加强基本的理解。应用的例子包括医疗磁共振成像仪（MRI）中的强超导磁体，用于基本粒子研究的大型强子对撞机环，超灵敏超导量子干涉探测器，使世界上最快的火车悬浮的超导/磁技术，以及通过超导电缆向居民区输电的示范项目。超导材料和性能的进一步发展有望加速创新向公共用途的过渡。除了研究之外，该奖项还将支持年轻科学家在科学技术研究、开发、教育和管理领域的职业发展道路的培训。技术概述高温超导理论六十年来一直处于理论凝聚态理论的最前沿。&一种新的高温超导体的发现将该领域推向了另一个不同的水平。一种方法是重新调整基本的科学范式，即：实验引导和刺激理论。对于这些预言，理论（主要是阿什克罗夫特的工作）出现在高压技术能够测试预测之前。硫化氢和相关电子的电子-声子机制可能被认为是合理理解的，但是最基本的量--运动质子引起的扰动以及它如何影响费米表面上的电子配对，特别是矩阵元素-它隐藏在复杂的计算机模拟中，没有提供任何能够预测和设计高温超导体的理解。或更低的压力。 该项目提出通过计算和分析费米表面上电子的这种逐原子散射来完成这种理解，通过对线性响应的数值评估来补充电子线性响应的传统理论。这些新的理解将促进合理的材料设计，而不是爱迪生式的发现，并通过揭示电子-声子矩阵元素的"基因组"来实现更好的超导体的真实的前景。这些进展将适用于其他超导材料的挑战，特别是单层硒化铁的挑战，人们普遍怀疑电子-声子耦合增强了潜在的基于磁性的配对机制。此外，硫化氢的非常高的Tc以及电子精细结构，这是使其特殊的一个重要特征，在模拟和基本理解行为（电子响应）方面提出了新的挑战，这些挑战超出了这种类型的电子配对的传统理论。该项目的结果预计将影响具有特定应用所需传输特性的新材料的预测，设计和控制，包括半导体和半金属，热电材料和优化的磁电系数。除了研究之外，该奖项还将支持年轻科学家在科学技术研究，开发，教育和管理领域的职业道路的培训。&

NONTECHNICAL SUMMARYThis award supports research and education to enhance our understanding of the relationship between how electrons respond to changes in their environment and their tendency to form pairs rather than to remain relatively independent. Pairing of electrons in solids lies at the root of several of the most interesting and useful properties of solids, with superconductivity and inhomogeneous magnetism being two important examples.The 2016 discovery of superconductivity with a critical onset temperature (Tc) above 200 K (-85 F) in trihydrogen sulfide has established a new record for Tc, promoting hydrogen-rich materials as the new frontier in this area of research. This revolution in high-temperature superconductivity comes at the expense of requiring an enclosed pressure cell to provide the two million atmospheres of pressure that induces superconductivity. For progress, theory and simulations must play a much larger role if higher Tc or lower pressure examples are to be discovered. Existing simulations for several candidate hydrides reveal the need to understand at a basic level the interaction of the metallic conduction electrons with a vibrating proton (hydrogen nucleus). This project will use this materials platform to address the fundamental question of why some hydrides are spectacular superconductors, while seemingly similar others are not. Analogous simulations will be applied to other peculiar superconductors (viz. single layers of iron selenide) where a related type of pairing is the best candidate for promoting impressive enhancements of superconducting critical temperatures. The principal investigator will extend and apply relevant theory, and write computer codes for calculations necessary in the study of this problem.By edging its way into technology, superconductivity is achieving broader impacts beyond enhanced fundamental understanding. Examples of applications include strong superconducting magnets in medical magnetic resonance imagers (MRI), the Large Hadron Collider ring used for elementary particle study, ultra-sensitive superconducting quantum interference detectors, superconducting/magnetic technology levitating the world's fastest trains, and demonstration projects for power transmission to residential areas through superconducting cables. Further developments in superconducting materials and properties promise to accelerate the transition of innovations to public use. In addition to research, this award will support the training of young scientists for career paths in science & technology research, development, education, and administration areas.TECHNICAL SUMMARYThe theory of high-temperature superconductivity has been at the forefront of theoretical condensed-matter theory for six decades. The discovery of a new class of high-Tc superconductors moves the field to another, different level. One way it does so is by readjusting the basic scientific paradigm, which has been: experiment leads and stimulates theory. For these hydrides, theory (primarily, Ashcroft's work) appeared well before high-pressure techniques became able to test predictions. The electron-phonon mechanism for hydrogen sulfide and related hydrides might be claimed to be reasonably understood, but the most fundamental quantity -the perturbation caused by a moving proton and how it effects pairing of electrons on the Fermi surface, specifically the matrix element- is hidden inside sophisticated computer simulations without providing any understanding that would enable prediction and design of outstanding superconductors at higher temperature or lower pressure. This project proposes to complete this understanding by calculating and analyzing this scattering atom-by-atom of electrons at the Fermi surface by complementing the conventional theory of electronic linear response with numerical evaluation of the linear response. The added understanding will promote rational material design, versus Edisonian discovery, and a real prospect of even better superconductors by revealing the "genome" of the electron-phonon matrix element. Advances will be applicable to other superconducting materials challenges, especially that of single-layer iron selenide, where it is widely suspected that electron-phonon coupling enhances the underlying, magnetically based, pairing mechanism. Additionally, the very high Tc of hydrogen sulfide together with the electronic fine structure, an important feature that makes it special, presents new challenges in the simulation and basic understanding of behavior (electronic response) that extends beyond the conventional theory of this type of electron pairing. The results of this project are expected to impact the prediction, design, and control of new materials with transport properties required for specific applications, including semiconductors and semimetals, thermoelectric materials, and optimized magnetoelectronic coefficients. In addition to research, this award will support the training of young scientists for career paths in science & technology research, development, education, and administration areas.