CAREER: Unconventional superconductivity and disordered criticality in two dimensions

职业：非常规超导性和二维无序临界性

• 批准号: 2341066
• 负责人: Alex Thomson
• 金额: $ 61万
• 依托单位: University of California-Davis
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2024
• 资助国家: 美国
• 起止时间: 2024-07-01 至 2029-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2341066&HistoricalAwards=false
• 关键词: CAREER; Unconventional; superconductivity; disordered; criticality

NON-TECHNICAL SUMMARYThis CAREER award supports theoretical research and education aimed at understanding quantum phases of electrons in two-dimensional materials, with a focus on superconductivity and disorder. Although certain phases of matter are well-described in colloquial terms, for example liquid or solid, the fundamentally quantum nature of the universe supports a multitude of states beyond those we see in everyday life. The quantum nature of these phases often results in incredible properties; for instance, a superconducting system conducts without resistance, allowing electricity to be transported over arbitrary distances without energy loss.Recent experimental progress offers an exciting opportunity to improve our understanding of quantum systems whose electrons interact with each other strongly (i.e., the electrons strongly ``feels'' the presence of their peers), a class of systems that have historically been very difficult to describe theoretically. Experimentalists have achieved unprecedented control over the fabrication of two-dimensional materials such as graphene (an intrinsically two-dimensional material composed of carbon) and assemblies made from them, allowing the construction of systems that realize a variety of quantum phases. These developments support a relatively rapid interplay between theory and experiment, which this project will exploit to improve our general understanding of quantum matter. Specifically, this project aims to:(1) Develop a unified understanding of the superconducting phases seen in a variety of distinct graphene structures, systems constructed by stacking graphene in different ways. The PI will use a variety of theoretical techniques to investigate models for superconductivity based on features common to all superconducting graphene systems.(2) Characterize quantum phase transitions in 2D with disorder, such as impurities and other imperfections in the arrangement of atoms. Disorder is an unavoidable feature of all material systems. Quantum phase transitions are driven by quantum fluctuations in contrast to more familiar transitions like ice to water that are driven by thermal fluctuations. The PI will specifically focus on the transitions separating two quantum phases of matter, where disorder can have especially subtle consequences. Integrated within this research project is a multi-level plan aimed at promoting physics to underrepresented groups both before and during undergraduate education. Specifically, the PI will (i) foster early interest in condensed matter among high school students by developing and teaching a course about 2D quantum materials for a summer Science Apprenticeship program at River City High; (ii) encourage and support aspiring young scientists at both a high school and undergraduate level through a partnership with various mentoring programs; and (iii) initiate an undergraduate peer-mentoring program aimed at students belonging to underrepresented groups.TECHNICAL SUMMARYThis CAREER award supports theoretical research and education into experimentally accessible properties of two-dimensional (2D) quantum phases of matter, focusing on superconducting graphene and the interplay of disorder and criticality.Theories of highly entangled quantum states of matter---their characterization and classification---have seen great strides in the past several decades. By contrast, an understanding of the prerequisites needed to physically realize these states and the criteria to identify them is lagging. An opportunity to narrow the gap between physical materials and theoretical understanding has recently arisen in the form of groundbreaking experimental developments in the synthesis and manipulation of true 2D materials, which have resulted in the discovery of a multitude of systems displaying a wide variety of correlated phases. The best-studied of these 2D systems are the van der Waals materials: not only can many different van der Waals systems be stacked in a nearly arbitrary fashion, but the twist angle between layers can also be specified. For sufficiently small twist angles, the result is a moiré superlattice orders of magnitude larger than the microscopic crystal of the constituent atoms. These advances provide a new set of tuning parameters---gating, stacking, and twist angle---to exploit in the pursuit of characterizing and understanding the ensuing quantum phenomena. The result is a relatively rapid interplay between theory and experiment, which this project will leverage in order to better understand the role of interactions, disorder, and their interplay in 2D systems. The specific aims of the project are:(1) The development of a unified understanding of superconducting graphene systems. Superconductivity has been observed in numerous graphene systems, both with and without moiré superlattices. The PI will investigate both the identity of the normal state parent to the superconductor as well as the superconducting pairing glue itself through a mix of analytical and numerical techniques.(2) An improved characterization and understanding of quantum critical points in 2D with disorder, drawing inspiration from recent experiments. The PI will both compute experimentally relevant observables as well as investigate the more formal question of disorder at a weak first order transition.Integrated within this research project is a multi-level plan aimed at promoting physics to underrepresented groups both before and during undergraduate education. Specifically, the PI will (i) foster early interest in condensed matter among high school students by developing and teaching a course about 2D quantum materials for a summer Science Apprenticeship program at River City High; (ii) encourage and support aspiring young scientists at both a high school and undergraduate level through a partnership with various mentoring programs; and (iii) initiate an undergraduate peer-mentoring program aimed at students belonging to underrepresented groups.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

该职业奖支持旨在理解二维材料中电子量子相的理论研究和教育，重点是超导性和无序性。虽然物质的某些相可以用通俗的术语很好地描述，例如液体或固体，但宇宙的基本量子性质支持我们日常生活中所见之外的许多状态。这些相的量子特性通常会产生令人难以置信的特性；例如，超导系统无电阻导电，允许电力在任意距离上传输而不损失能量。最近的实验进展提供了一个令人兴奋的机会来提高我们对量子系统的理解，这些系统的电子相互作用强烈（即，电子强烈地“感觉”到它们的同伴的存在），这是一类历史上很难从理论上描述的系统。实验学家已经实现了对二维材料制造的前所未有的控制，如石墨烯（本质上是一种由碳组成的二维材料）和由它们制成的组件，允许构建实现各种量子相的系统。这些发展支持理论和实验之间相对快速的相互作用，这个项目将利用它来提高我们对量子物质的一般理解。具体而言，该项目旨在：(1)对各种不同石墨烯结构（通过不同方式堆叠石墨烯构建的系统）中的超导相形成统一的理解。PI将使用各种理论技术来研究基于所有超导石墨烯系统共同特征的超导模型。(2)表征二维无序的量子相变，如杂质和原子排列中的其他缺陷。无序是所有物质系统不可避免的特征。量子相变是由量子涨落驱动的，相比之下，我们更熟悉的冰到水的转变是由热涨落驱动的。PI将特别关注分离物质的两个量子相的转变，其中的无序可能会产生特别微妙的后果。在这个研究项目中整合了一个多层次的计划，旨在在本科教育之前和期间向代表性不足的群体推广物理学。具体来说，PI将(i)通过为River City高中的暑期科学学徒计划开发和教授2D量子材料课程，培养高中生对凝聚态物质的早期兴趣；（ii）通过与各种指导计划的合作，鼓励和支持有抱负的高中和本科水平的年轻科学家；（三）启动针对弱势群体学生的大学生同伴辅导项目。该职业奖支持物质二维（2D）量子相实验可获得特性的理论研究和教育，重点是超导石墨烯以及无序和临界的相互作用。物质高度纠缠量子态的理论——它们的表征和分类——在过去的几十年里取得了巨大的进步。相比之下，对物理上实现这些状态所需的先决条件和识别它们的标准的理解是滞后的。最近出现了一个缩小物理材料和理论理解之间差距的机会，在合成和操纵真正的二维材料方面取得了突破性的实验进展，这导致发现了许多显示各种相关相的系统。这些二维体系中研究得最好的是范德华材料：不仅许多不同的范德华体系可以以几乎任意的方式堆叠，而且层之间的扭转角也可以指定。对于足够小的扭转角，结果是一个比组成原子的微观晶体大几个数量级的莫尔维尔超晶格。这些进展提供了一组新的调谐参数-门控，堆叠和扭转角-用于追求表征和理解随后的量子现象。结果是理论和实验之间相对快速的相互作用，这个项目将利用它来更好地理解相互作用，无序，以及它们在二维系统中的相互作用。该项目的具体目标是：(1)发展对超导石墨烯系统的统一理解。在许多石墨烯体系中，无论有无摩尔超晶格，都可以观察到超导性。PI将通过分析和数值技术的混合研究超导体的正常状态母体以及超导配对胶本身的身份。(2)从最近的实验中获得灵感，改进了二维无序量子临界点的表征和理解。PI将计算实验相关的可观测值，并研究弱一阶跃迁中更正式的无序问题。在这个研究项目中整合了一个多层次的计划，旨在在本科教育之前和期间向代表性不足的群体推广物理学。具体来说，PI将(i)通过为River City高中的暑期科学学徒计划开发和教授2D量子材料课程，培养高中生对凝聚态物质的早期兴趣；（ii）通过与各种指导计划的合作，鼓励和支持有抱负的高中和本科水平的年轻科学家；（三）启动针对弱势群体学生的大学生同伴辅导项目。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。