Quantum Phase Transitions: Disorder, Dynamics, and Frustration

该奖项由2009年美国复苏和再投资法案(公法111-5)资助。技术总结该奖项支持相关量子材料和纳米结构的理论研究和教育。由于量子涨落、各种相互作用、量子限制和无序之间的竞争，这些现象显示出丰富多样的新现象。在这些系统中，分隔不同基态相的量子相变起着重要作用，至少有两个原因。一方面，它们的特殊性质可以控制很大一部分参数空间。另一方面，它们为理解复杂量子系统的整个相图提供了一个新的视角，这是对传统微扰方法的补充。本方案的主要目标是探索各种量子材料中的量子相变，主要集中在三个方面：1.量子相变和猝灭无序：PI将关注一阶量子相变中的无序效应，包括有序-无序类型的相变以及竞争基态有序之间的相变。受最近在Ce-Pd-Ru体系和Ni-V体系中有趣的实验的启发，PI将分析无序巡回铁磁转变。量子临界点的动力学和输运：PI将研究超薄MOGe和Nb纳米线中超导体-金属转变的输运特性。PI将发展金属铁磁体和反铁磁体的Griffiths磁相中的电子输运理论。几何受阻磁体中的量子相变：PI计划研究简并、涨落和无序之间的相互作用如何在几何受阻量子磁体中产生新的相，他将研究这些相之间的量子相变。为了进行这项研究，PI将使用包括平均场理论、微扰和强无序重整化群在内的分析技术和计算机模拟，包括经典和量子蒙特卡罗方法、数值重整化群。本科生将参与这项研究。为了帮助缩小课堂和研究之间的差距，他打算用一门高性能科学计算研讨会课程来补充他的计算物理课程，这门课程对吸引本科生很有帮助。该研讨会课程旨在将来自不同学科的感兴趣的密苏里州S大学的学生聚集在一起。国际和平研究所还计划建立一系列诺贝尔奖演讲。将在每年秋天诺贝尔物理学奖公布后颁发。这些讲座将对该奖项背后的物理学作一个初步的介绍，在非理科专业的学生和高中生都能达到的水平上。这一系列将有助于向更广泛的受众传播科学的兴奋。非技术总结该奖项支持材料中电子相互作用特别强烈的一个重要方面的理论研究和教育。这些材料经常表现出许多不同的相，例如不同种类的磁性和超导电性？物质的一种电子状态，它对电流的流动没有阻力。这些相可能被一种不寻常的相变分开，这种相变发生在绝对零度，称为量子相变。分离相可以在很大的温度范围内控制材料的电子性质。PI将使用先进的理论方法和计算机模拟来研究晶格中的缺陷对这些量子临界点的影响，以及分隔新物质状态的量子临界点附近的电子态的性质。这项研究将有助于我们理解一类有趣的、不断增长的材料，这些材料展示了物质的新电子状态和新现象，为可能的新电子设备技术提供了智力基础。本科生将参与这项研究。为了帮助缩小课堂和研究之间的差距，他打算用一门高性能科学计算研讨会课程来补充他的计算物理课程，这门课程对吸引本科生很有帮助。该研讨会课程旨在将来自不同学科的感兴趣的密苏里州S大学的学生聚集在一起。国际和平研究所还计划建立一系列诺贝尔奖演讲。将在每年秋天诺贝尔物理学奖公布后颁发。这些讲座将对该奖项背后的物理学作一个初步的介绍，在非理科专业的学生和高中生都能达到的水平上。这个系列将有助于向更广泛的受众传播科学的激动人心。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).TECHNICAL SUMMARYThis award supports theoretical research and education on correlated quantum materials and nanostructures. These show a rich variety of novel phenomena due to the competition between quantum fluctuations, various interactions, quantum confinement and disorder. The quantum phase transitions that separate the different ground state phases in these systems play an important role for at least two reasons. On the one hand, their peculiar properties can control large parts of parameter space. On the other hand, they provide a novel perspective for understanding the entire phase diagram of a complex quantum system which is complimentary to traditional perturbative approaches.The major objective of this proposal is to explore quantum phase transitions in a variety of quantum materials, concentrating on three areas:1. Quantum phase transitions and quenched disorder: The PI will focus on disorder effects at first-order quantum phase transitions including those of the order-disorder type as well as transitions between competing ground state orders. Motivated by recent interesting experiments in cerium-palladium-ruthenium systems and nickel-vanadium systems, the PI will analyze the disordered itinerant ferromagnetic transition.2. Dynamics and transport at quantum critical points: The PI will study the transport properties at the superconductor-metal transition in ultrathin MoGe and Niobium nanowires. The PI will develop a theory of electronic transport in the magnetic Griffiths phases of metallic ferromagnets and antiferromagnets.3. Quantum phase transitions in geometrically frustrated magnets: The PI plans to investigate how the interplay between degeneracy, fluctuations and disorder leads to novel phases in geometrically frustrated quantum magnets, and he will study the quantum phase transitions between these phases.To carry out the research, the PI will use a combination of analytical techniques, including mean-field theory, perturbative and strong-disorder renormalization groups, and computer simulations, including classical and quantum Monte-Carlo methods, numerical renormalization group.Undergraduate students will be involved in the research. To help close the gap between classroom and research, the PI intends to complement his computational physics course, which has been instrumental for attracting undergraduates, with a seminar course on high-performance scientific computing aimed at bringing together the interested Missouri S&T students from various disciplines. The PI also aims to establish a series of ?Nobel Prize talks? to be given each fall after the Physics Nobel Prize has been announced. These talks will give an elementary introduction into the physics behind the prize, at a level accessible for non-science majors and high-school students. This series would help disseminate the excitement of science to a broader audience.NON-TECHNICAL SUMMARYThis award supports theoretical research and education on an important aspect of materials in which electrons interact with each other particularly strongly. These materials often exhibit many different phases such as different kinds of magnetism and superconductivity ? an electronic state of matter which exhibits no resistance to the flow of electricity. These phases may be separated by an unusual kind of phase transition which takes place at the absolute zero of temperature called a quantum phase transition. The points that separate phases can control the electronic properties of materials over a wide range of temperature. The PI will use advanced theoretical methods and computer simulations to study the effect of imperfections in the crystal lattice on these quantum critical points and the properties of the electronic states near quantum critical points that separate novel states of matter. The research will contribute to our understanding of an interesting and growing class of materials that display new electronic states of matter and new phenomena that provide the intellectual foundations for possible new electronic device technologies.Undergraduate students will be involved in the research. To help close the gap between classroom and research, the PI intends to complement his computational physics course, which has been instrumental for attracting undergraduates, with a seminar course on high-performance scientific computing aimed at bringing together the interested Missouri S&T students from various disciplines. The PI also aims to establish a series of ?Nobel Prize talks? to be given each fall after the Physics Nobel Prize has been announced. These talks will give an elementary introduction into the physics behind the prize, at a level accessible for non-science majors and high-school students. This series would help disseminate the excitement of science to a broader audience.