CAREER: Quantum Phase Transitions in Electronic Systems

该职业奖支持凝聚态物理的理论和计算研究，并开发计算物理课程，使用计算来提高对物理的理解。研究将沿着三个独立但相关的路线进行，其共同目标是研究接近量子相变的电子系统。首先，将用场论方法研究干净和弱无序流动电子的磁性和超导跃迁。重点将放在临界和非临界软模式的耦合上，这可以极大地改变临界行为。PI的目标是为这些跃迁开发一个费米子和玻色子的组合重整化群，其中包括所有同等基础的软模式。这一理论也将允许对接近跃迁的输运进行量子力学描述。这项工作不仅对量子相变界具有根本意义，而且对重费米子材料、弱铁磁体和其他奇异超导体也具有直接的实验意义。第二方面的研究致力于研究淬火失序的非扰动效应。PI最近发现一些具有伊辛对称的量子相变（包括流动的量子反铁磁相变）被无序所掩盖。本文提出利用极值统计、实空间重整化和渗透思想以及蒙特卡罗模拟来研究这种激励效应的性质和后果。将开发特殊的抽样技术来调查与强无序系统相关的广泛分布。单独的项目将致力于连续对称的过渡，没有涂抹，而是非常规的强无序固定点。除了它与一些重费米子系统的直接关联之外，在这些系统中已经观察到圆跃迁的迹象，这项工作将对无序系统的统计物理学和其他处理罕见事件和大涨落的领域产生兴趣。第三条研究路线，涉及无序电子微观模型的计算机模拟，补充了关于非微扰无序效应的工作。第一个应用将是研究一个巡回磁量子相变的单个稀有区域的性质及其与脏金属体系中相关诱导的局域磁矩的关系。PI打算开发一系列针对高年级本科生和初级研究生的计算物理课程。在这些课程中，学生将学习如何使用计算和模拟来推进对物理的理解。这涉及的技能通常不会在物理入门课程中教授，因为学生通常缺乏编程背景，而且通常不会在强调计算技术方面的计算机科学和数学课程中教授。这些以物理为中心的课程旨在填补这一空白。它们在教授计算物理方面的作用类似于传统的实验课程，让学生在计算工作的各个方面都有实际的经验。成功完成课程的学生应在当今的就业市场上获得高度市场化的跨学科技能，并为参与PI的研究以及物理系的其他研究项目做好充分准备。这将为即将入学的研究生提供一个良好的开端，并有助于为处于科学前沿的本科生提供研究机会。此外，也希望这些课程将有助于吸引新的学生到物理专业。在培养本科生和吸引新人才进入物理学领域方面有更广泛的影响。在理解强相关电子系统和量子临界现象方面取得的进展，可能为未来的技术奠定基础，并可能影响其他领域，特别是物理学的其他领域。该职业奖支持凝聚态物理的理论和计算研究，并开发计算物理课程，使用计算来提高对物理的理解。PI将研究量子相变附近的完美和无序电子系统。量子相变发生在零度。普通相变是由热波动驱动的。相比之下，量子相变是由量子力学波动驱动的。它们可以在有限的温度下产生不寻常的性质，并可能为迄今为止难以解释的强相关电子材料的奇异性质提供见解。PI计划研究铁磁和超导量子相变，并调查无序的影响。PI打算开发一系列针对高年级本科生和初级研究生的计算物理课程。在这些课程中，学生将学习如何使用计算和模拟来推进对物理的理解。这涉及的技能通常不会在物理入门课程中教授，因为学生通常缺乏编程背景，而且通常不会在强调计算技术方面的计算机科学和数学课程中教授。这些以物理为中心的课程旨在填补这一空白。它们在教授计算物理方面的作用类似于传统的实验课程，让学生在计算工作的各个方面都有实际的经验。成功完成课程的学生应在当今的就业市场上获得高度市场化的跨学科技能，并为参与PI的研究以及物理系的其他研究项目做好充分准备。这将为即将入学的研究生提供一个良好的开端，并有助于为处于科学前沿的本科生提供研究机会。此外，也希望这些课程将有助于吸引新的学生到物理专业。在培养本科生和吸引新人才进入物理学领域方面有更广泛的影响。在理解强相关电子系统和量子临界现象方面取得的进展，可能为未来的技术奠定基础，并可能影响其他领域，特别是物理学的其他领域

This CAREER award supports theoretical and computational research in condensed matter physics and developing computational physics courses that use computation to advance understanding of physics.Research will be conducted along three separate but related lines with a common objective to investigate electronic systems near quantum phase transitions. In the first line, magnetic and superconducting transitions of clean and weakly disordered itinerant electrons will be studied using field-theoretic methods. Emphasis will be on the coupling of critical and noncritical soft modes which can dramatically change critical behavior. The PI aims to develop a combined fermionic and bosonic renormalization group for these transitions that includes all soft modes on equal footing. This theory will also permit a quantum mechanical description of transport close to the transition. This work will not only be of fundamental interest for the quantum phase transition community, it also has direct experimental relevance for heavy fermion materials, weak ferromagnets, and other exotic superconductors. The second line of research is devoted to non-perturbative effects of quenched disorder. The PI recently found that some quantum phase transitions with Ising symmetry (including the itinerant quantum antiferromagnetic one) are smeared by disorder. It is proposed to investigate the properties and consequences of this exciting effect by extremal statistics, real-space renormalization and percolation ideas as well as Monte-Carlo simulations. Special sampling techniques will be developed to investigate broad distributions associated with strongly disordered systems. Separate projects will be devoted to transitions with continuous symmetry where no smearing is expected but rather unconventional strong-disorder fixed points. Beyond its direct relevance for some heavy fermion systems, where indications of a rounded transition have been observed, this work will be of interest for the statistical physics of disordered systems and for other areas dealing with rare events and large fluctuation.The third research line, involving computer simulations of microscopic models of disordered electrons, complements the work on non-perturbative disorder effects. A first application will be to investigate the properties of a single rare region of an itinerant magnetic quantum phase transition and its relation to a correlation-induced localized magnetic moment in a dirty metallic system.The PI intends to develop a sequence of computational physics courses aimed at upper level undergraduate and beginning graduate students. In these courses, the students will learn how to use computation and simulation to advance the understanding of physics. This involves skills that are typically not taught in introductory physics courses where students often lack the background in programming and that are typically not taught in computer science and mathematics courses which emphasize technical aspects of computation. These physics-centered courses are aimed at filling this gap. Their role for teaching computational physics is similar to that of traditional laboratory courses for experiment, giving the students hands-on experience in all aspects of computational work. Students who successfully finish the courses should acquire highly marketable interdisciplinary skills in today's job market and should be well prepared to participate in the PI's research as well as other research projects in the physics department. This will give incoming graduate students a head start and help to provide research opportunities for undergraduate students at the forefront of science.In addition, it is also hoped that these course will help attract new students to the physics program.There are broader impacts in the area of educating undergraduates and in attracting new talent to the field of physics. Advances in understanding strongly correlated electron systems and quantum critical phenomena contribute concepts that may lay the foundation for future technologies and may impact other fields, particularly other areas of physics.%%%This CAREER award supports theoretical and computational research in condensed matter physics and developing computational physics courses that use computation to advance understanding of physics.The PI will investigate perfect and disordered electronic systems near quantum phase transitions. Quantum phase transitions occur at zero temperature. Ordinary phase transitions are driven by thermal fluctuations. By contrast, quantum phase transitions are driven by quantum mechanical fluctuations. They can give rise to unusual properties at finite temperature and may provide insight into exotic properties of strongly correlated electron materials that have so far resisted explanation. The PI plans to study ferromagnetic and superconducting quantum phase transitions and to investigate the effect of disorder.The PI intends to develop a sequence of computational physics courses aimed at upper level undergraduate and beginning graduate students. In these courses, the students will learn how to use computation and simulation to advance the understanding of physics. This involves skills that are typically not taught in introductory physics courses where students often lack the background in programming and that are typically not taught in computer science and mathematics courses which emphasize technical aspects of computation. These physics-centered courses are aimed at filling this gap. Their role for teaching computational physics is similar to that of traditional laboratory courses for experiment, giving the students hands-on experience in all aspects of computational work. Students who successfully finish the courses should acquire highly marketable interdisciplinary skills in today's job market and should be well prepared to participate in the PI's research as well as other research projects in the physics department. This will give incoming graduate students a head start and help to provide research opportunities for undergraduate students at the forefront of science.In addition, it is also hoped that these course will help attract new students to the physics program.There are broader impacts in the area of educating undergraduates and in attracting new talent to the field of physics. Advances in understanding strongly correlated electron systems and quantum critical phenomena contribute concepts that may lay the foundation for future technologies and may impact other fields, particularly other areas of physics.***