Simulation studies of ground state phases and criticality in correlated quantum matter

相关量子物质中基态相和临界性的模拟研究

• 批准号: 1104708
• 负责人: Anders Sandvik
• 金额: $ 37.5万
• 依托单位: Trustees of Boston University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-09-01 至 2014-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1104708&HistoricalAwards=false
• 关键词: Simulation; studies; ground; state; phases

TECHNICAL SUMMARYThis award supports research and related educational activities in computational quantum many-body physics, with a focus on collective quantum phenomena in spin systems. Quantum spin systems are important models for describing the magnetic properties of Mott insulators. In addition to their important role in direct modeling of experimentally studied materials, quantum spin models can also be used as simplified prototypical models capturing essential physics of various many-body phenomena that are currently subjects of ongoing theoretical and computational investigations. The main objective of this award is to gain new generic insights into the physics of collective quantum many-body states through unbiased computer simulations, primarily using quantum Monte Carlo methods. Of particular interest are quantum phase transitions, phase transitions that take place at zero temperature with associated scaling behavior also at finite temperature, as a function of some model parameter that regulates the strength of the quantum fluctuations in the system. The PI has devised a class of spin-one-half lattice systems in which the standard antiferromagnetic Heisenberg exchange interaction is supplemented by multi-spin interactions engineered to destroy the antiferromagnetic order. This transition in two dimensions may be associated with fractionalization of elementary excitations. Normally, the excitations of the Neel state are spin waves carrying spin one, and in the valence-bond-solid state there are gapped spin-one "triplon" excitations. However, close to the phase transition, previous analytical and numerical studies indicate that these excitations may fractionalize into spinons carrying spin-one-half. This deconfinement of spinons has far reaching consequences both for the theoretical description of the phase transition and for experimental signatures of it. Spinons may play an important role in many strongly-correlated electron systems, for example in the "strange metal" state of underdoped high-Tc superconductors. The PI is carrying out quantum Monte Carlo studies in order to characterize the nature of the spinons and their manifestations in physical observables. Both pristine and disordered systems are considered. Work on novel and improved simulation methods will be carried out as an integral part of the award. The methods to be developed through this award are contributing to the emerging "toolbox" of software enabling simulations of magnetic properties of Mott insulators. These methods have broader applicability, beyond the main scientific questions addressed, and are of interest in other fields, for example studies of ultracold atoms in optical lattices and in quantum information theory. Graduate students supported by this award will receive training in these advanced methods and their applications. The PI is also actively teaching graduate students and postdoctoral researchers at summer schools, and is also developing on-line instructional material for learning quantum Monte Carlo simulations and other numerical many-body techniques.NON-TECHNICAL SUMMARYThis award supports research and related educational activities in computer simulation studies of quantum spin models. These systems of interacting microscopic magnetic moments represent electrons localized at individual atoms or molecules in certain electrically insulating materials. Various magnetic properties can be achieved, depending on the crystal structure and the chemical composition of the material. The objective of the award is to carry out computer simulation studies to aid experimental investigations carried out by other researchers, as well as to study fundamental aspects of the model systems to gain further insights into what kind of properties are possible to achieve in principle. These simulations relate to existing analytical theories and influence developing theoretical concepts. In analogy with the three common phases of matter encountered in daily life - liquid, solid, and gas - a system of a large number of electronic spins can also from different phases. The possibilities are very rich, with many different phases analogous to the three common ones. Spins can "solidify" into states in which the individual electronic magnetic moments or pairs of moments form various regular patterns. These patterns can "melt" at phase transitions where new liquid-like spin states appear. Understanding these quantum phases and quantum phase transitions is very challenging and important, both from a fundamental scientific perspective and for ultimate technological applications involving the special properties of electronic spins. The PI has previously developed computational methods and devised a class of spin models in which certain magnetic quantum phase transitions can be studied in unprecedented detail. The PI will study the nature of the elementary excitations of spin systems close to quantum phase transitions. An excitation can be thought of as a defect propagating as a wave through the system. These waves carry certain amounts of magnetic moment and normally there is a smallest unit of it. An exciting possibility with both experimental and theoretical consequences, is that this smallest unit can split up into two independently propagating waves. The PI is investigating these spinons in model systems. Information gained from computer simulations will give unique insights into the properties of these intriguing quantum entities and the role they play in various circumstances. New and improved computational methods will be developed to this research. These computational tools will contribute to the software infrastructure of computational quantum physics. Graduate students supported by the award are developing expertise in advanced simulation methods and many-body quantum physics. The PI is also actively involved in various other educational activities, including lecturing at international summer schools and developing pedagogical on-line material for learning the advanced computational techniques related to the award.

技术摘要该奖项支持计算量子多体物理领域的研究和相关教育活动，重点关注自旋系统中的集体量子现象。量子自旋系统是描述莫特绝缘体磁特性的重要模型。除了在实验研究材料的直接建模中发挥重要作用外，量子自旋模型还可以用作简化的原型模型，捕获各种多体现象的基本物理现象，这些现象是目前正在进行的理论和计算研究的主题。该奖项的主要目标是通过无偏计算机模拟（主要使用量子蒙特卡罗方法）获得对集体量子多体态物理学的新的普遍见解。特别令人感兴趣的是量子相变，即在零温度下发生的相变，以及在有限温度下的相关缩放行为，作为调节系统中量子涨落强度的某些模型参数的函数。 PI 设计了一类自旋半晶格系统，其中标准反铁磁海森堡交换相互作用被设计为破坏反铁磁秩序的多自旋相互作用所补充。 这种二维转变可能与基本激发的细分有关。通常，尼尔态的激发是携带自旋一的自旋波，而在价键固态中存在有间隙的自旋一“三联体”激发。然而，在接近相变时，先前的分析和数值研究表明，这些激发可能会分解成携带自旋一半的自旋子。自旋子的这种解除限制对于相变的理论描述和实验特征都具有深远的影响。自旋子可能在许多强相关电子系统中发挥重要作用，例如在欠掺杂高温超导体的“奇怪金属”态中。 PI 正在进行量子蒙特卡罗研究，以表征自旋子的性质及其在物理可观测值中的表现。原始系统和无序系统都被考虑。 新颖和改进的模拟方法的工作将作为该奖项的一个组成部分进行。通过该奖项开发的方法正在为新兴的软件“工具箱”做出贡献，从而能够模拟莫特绝缘体的磁性。这些方法具有更广泛的适用性，超出了所解决的主要科学问题，并且在其他领域也很有趣，例如光学晶格中的超冷原子和量子信息论的研究。 受该奖项支持的研究生将接受这些先进方法及其应用的培训。 PI 还积极在暑期学校教授研究生和博士后研究人员，并正在开发用于学习量子蒙特卡罗模拟和其他数值多体技术的在线教学材料。非技术摘要该奖项支持量子自旋模型计算机模拟研究中的研究和相关教育活动。这些相互作用的微观磁矩系统代表位于某些电绝缘材料中单个原子或分子处的电子。根据材料的晶体结构和化学成分，可以实现各种磁性。该奖项的目的是进行计算机模拟研究，以帮助其他研究人员进行实验研究，并研究模型系统的基本方面，以进一步了解原则上可以实现哪些属性。这些模拟与现有的分析理论相关并影响理论概念的发展。 与日常生活中遇到的三种常见物质相（液体、固体和气体）类似，大量电子自旋的系统也可以来自不同的相。可能性非常丰富，有许多不同的阶段类似于三个常见阶段。 自旋可以“固化”成各个电子磁矩或磁矩对形成各种规则模式的状态。这些图案可以在相变时“熔化”，出现新的类液体自旋态。无论是从基础科学角度还是涉及电子自旋特殊性质的最终技术应用来看，理解这些量子相和量子相变都是非常具有挑战性和重要的。 PI 之前开发了计算方法并设计了一类自旋模型，可以在其中以前所未有的细节研究某些磁量子相变。 PI 将研究接近量子相变的自旋系统基本激发的性质。激励可以被认为是作为波在系统中传播的缺陷。这些波携带一定量的磁矩，通常有一个最小的单位。具有实验和理论结果的令人兴奋的可能性是，这个最小的单元可以分裂成两个独立传播的波。 PI 正在研究模型系统中的这些自旋子。从计算机模拟中获得的信息将为这些有趣的量子实体的属性以及它们在各种情况下发挥的作用提供独特的见解。 这项研究将开发新的和改进的计算方法。这些计算工具将有助于计算量子物理的软件基础设施。受该奖项支持的研究生正在发展先进模拟方法和多体量子物理学方面的专业知识。 PI 还积极参与各种其他教育活动，包括在国际暑期学校讲授以及开发在线教学材料，以学习与该奖项相关的高级计算技术。