Electron Pairing in Doped Insulators

该奖项支持旨在理解一类掺杂高温超导体的超导机制的计算研究，即在25-30 K温度范围内超导的二维化合物LiHfNCl和三维绝缘体BaKBiO 3。 与低温重费米子超导体或高温超导铜酸盐和铁磷属元素化物不同，其中在超导状态附近和内部存在强磁性行为，并且大多数研究人员期望配对机制涉及磁性，这类掺杂绝缘体高温超导体不包含任何磁性离子，并且电子-声子耦合太弱而不能解释它们的高临界温度。 该项目解决了这种材料中出现的情况，其中相对低密度的掺杂载流子在高电荷移动离子的背景下动态相互作用。有效的电子-电子相互作用被其他电子和运动的离子屏蔽。 通过随机相位近似处理屏蔽的常规方法是不够的，因为它错过了由强相互作用的弱短程屏蔽产生的重要短程相关，并且给出了整体弱耦合。理论上的方法将是延长治疗的介电屏蔽矩阵超出平均场，从而耦合的离子和载体的筛选过程。这些研究的潜在回报是对一种新的配对机制的详细了解，这种机制在30 K下产生超导性，并且可能是产生更高临界温度的良好候选者。这项研究的一个重要成果可能通过可持续的绿色能源产生社会影响，这是新超导体的潜在发现和设计。该奖项还支持在计算凝聚态物理学前沿领域的研究生和博士后研究助理的教育，并将有助于培养年轻科学家，他们将构成未来的科学和技术劳动力。非技术概述该奖项支持旨在了解一类材料的计算研究，这些材料的组成LiHfNCl和BaKBiO 3通常不导电，在低温下进入一个阶段，电流在其中流过而没有任何电阻，使它们成为超导体。 与一些更常见的超导体不同，在这些超导体中，电子与带正电的原子核的振动的强烈相互作用最终导致了它们的超导特性，这些材料中的电子-原子核相互作用不足以解释它们成为超导体的观测温度。了解最新和最奇特的超导体仍然是凝聚态理论的知识前沿。在这个项目中，PI和他的团队将发展理论，并进行必要的大规模计算，以处理电子相互作用以及与高电荷移动离子相互作用时的动力学行为，最终目标是捕获这些材料成为超导体的基本机制。这项研究的一个重要成果可能会通过可持续的绿色能源产生社会影响，这就是新超导体的潜在发现和设计。该奖项还支持在计算凝聚态物理学前沿的研究生和博士后研究助理的教育，并将有助于培养年轻科学家谁将形成明天的科学和技术劳动力。

TECHNICAL SUMMARYThis award support computational research aimed at understanding the superconducting mechanisms of a class of doped high temperature superconductors, namely the two dimensional compound LiHfNCl and the three dimensional insulator BaKBiO3 that superconduct in the 25-30 K temperature range. Unlike low-temperature heavy fermion superconductors or the high temperature superconducting cuprates and iron pnictides, in which there is strong magnetic behavior near and within the superconducting state and a majority of researchers expect the pairing mechanism to involve magnetism, this class of doped-insulator high temperature superconductors do not contain any magnetic ions, and the electron-phonon coupling is too weak to account for their high critical temperatures. This project addresses the situation that arises in such materials where a relatively low density of doped carriers interact dynamically within a background of highly charged moving ions. The effective electron-electron interaction is screened both by other electrons and by the moving ions. The conventional means of handling screening, via the random phase approximation, is insufficient, as it misses important short-range correlations resulting from weak short-range screening of strong interactions, and gives an overall weak coupling. The theoretical approach will be to extend the treatment of the dielectric screening matrix beyond the mean field, thereby coupling the screening process of the ions and the carriers. The potential payoff for these investigations is a detailed understanding of a new pairing mechanism that produces superconductivity at 30 K and might be a good candidate to produce substantially higher critical temperatures.An important outcome of this research that could have a societal impact through sustainable green-energy is the potential discovery and design of new superconductors. This award also supports the education of a graduate student and a postdoctoral research associate at the frontiers of computational condensed matter physics, and will contribute to the training of young scientists who will form tomorrow's scientific and technological workforce.NONTECHNICAL SUMMARYThis award support computational research aimed at understanding how a class of materials with composition LiHfNCl and BaKBiO3, which do not normally conduct electricity, enter a phase at low temperatures wherein electricity flows through them without any resistance, making them superconductors. Unlike some of the more commonly known superconductors in which the strong interaction of the electrons with the vibrations of the positively charged nuclei are ultimately responsible for their superconducting properties, the electron-nuclei interaction in these materials is not strong enough to account for the observed temperatures at which they become superconducting. Understanding the newest and most exotic superconductors remains at the intellectual frontier of condensed matter theory. In this project, the PI and his group will develop the theory and perform the necessary large-scale computations to treat dynamical behavior of electrons as they interact with each other and with highly charged moving ions with the ultimate goal of capturing the essential mechanism through which these materials become superconducting. An important outcome of this research that could have a societal impact through sustainable green-energy is the potential discovery and design of new superconductors. This award also supports the education of a graduate student and a postdoctoral research associate at the frontiers of computational condensed matter physics, and will contribute to the training of young scientists who will form tomorrow's scientific and technological workforce.