Visualizing nanoscale phenomena in layered chalcogenides with heavy elements

非技术文摘在发现各种具有增强功能的新材料方面取得了巨大进展。然而，功能材料的技术应用要求对功能材料的组成和缺陷进行严格的控制。缺陷，特别是点缺陷的控制对半导体器件的性能至关重要，半导体器件是所有现代电子设备(如计算机、手机等)的基础。然而，直接探测和检测功能材料中的单个点缺陷是出了名的困难。扫描隧道显微镜(STM)是为数不多的允许科学家直接探测原子尺度现象的工具之一，包括点缺陷和局部电子性质的响应。本项目研究在合成过程中有意或无意地引入到块体材料中的点缺陷对称为层状硫化物的新型电子材料的影响。利用扫描隧道显微镜在纳米尺度上可视化有趣的电子现象，主要研究人员的目标是对这些功能材料中的驱动机制和点缺陷的控制有基本的了解。研究生和本科生的教育和培训与研究活动无缝结合，使他们能够学习基础材料科学，掌握先进的显微技术，更重要的是学习独立思考。该项目还通过各种计划，如阿雷斯蒂研究中心研究计划和罗格斯大学本科生研究体验计划，以及通过自由科学中心的科学伙伴计划，整合了对不具代表性的本科生的教育和培训。技术摘要层状硫化物一直是凝聚态物理中各种相关现象的活跃场所，范围从电荷密度波到超导电性。在层状硫族化合物中加入重元素会导致强的自旋-轨道耦合或二聚化的额外扭曲，导致出现诸如拓扑绝缘体和二聚化诱导的条纹调制等现象。这个项目解决了点缺陷(无论是内在的还是外在的)对这些迷人现象的影响，以获得对其驱动机制的基本了解。拓扑绝缘体是一种新的物质量子态，由于电子波函数的非平凡拓扑，绝缘体态被导电表面态包围。众所周知，拓扑绝缘体中的本征缺陷会导致大量的体导，这不利于与拓扑表面态相关的奇异现象的观察和技术应用。化学不均匀性的影响对于从根本上理解化学掺杂引起的“拓扑相变”至关重要。该项目的目标是识别和控制层状硫化物拓扑绝缘体(如Bi2Se3和Sb2Te3)中的本征和/或外在点缺陷。此外，这个项目的目的是全面了解重硫系化合物IrTe2中出现的多条纹调制的机制，这种调制与竞争相互作用导致的魔鬼阶梯现象密切相关。这些材料中的原子级缺陷、电子调制和纳米级不均匀性被可视化，并使用最先进的扫描隧道显微镜和光谱学进行检测。这些研究工作得到了大量探测器、第一性原理计算和通过国内和国际合作进行的理论建模的赞扬。

Nontechnical Abstract Tremendous progress has been made on discovering various new materials with enhanced functionalities. The technological applications of functional materials, however, demand extreme control of composition and imperfections of functional materials. The control of defects, especially point defects is crucial for the performance of semiconductor devices, which are building blocks of all modern electronics such as computers, cell phones, etc. Yet it is notoriously difficult to directly probe and exam individual point defects in functional materials. Scanning tunneling microscope (STM) is one of the few tools that allow scientists to directly probe atomic scale phenomena, including point defects and responses of local electronic properties. This project investigates the impacts of point defects, either intentionally or unintentionally introduced to bulk materials during synthesis, on novel electronic materials called layered chalcogenides. Using STM to visualize interesting electronic phenomena at nanometer scale, the principle investigator aims to obtain fundamental understandings of the driving mechanisms and the control of point defects in these functional materials. Education and training of graduate and undergraduate students is seamlessly integrated to the research activities, which enable them to learn fundamental material science, to master advanced microscopic techniques, and more importantly, to learn independent thinking. This project also integrates education and training of under-representative undergraduate students through various programs such as Aresty Research Center research program and Research Experiences for Undergraduates program at Rutgers, and of high school students through the Partner in Science program of Liberty Science Center. Technical AbstractLayered chalcogenides have been the active playground for various correlated phenomena in condensed matter physics, ranging from charge density wave and superconductivity. Incorporating heavy elements in layered chalcogenides introduces additional twists of strong spin-orbital coupling or dimerization, leading to emergent phenomena such as topological insulators and dimerization induced stripe modulations. This project addresses the impact of point defects (either intrinsic or extrinsic) on these fascinating phenomena to gain fundamental understanding of their driving mechanisms. Topological insulators are new quantum states of matter where insulating bulk states are surrounded by conducting surface states because of nontrivial topology of electronic wave functions. Native defects in topological insulators are known to induce substantial bulk conduction, which is detrimental for the observation and technological applications of exotic phenomena related to topological surface states. The influence of chemical inhomogeneity is crucial for fundamental understanding of "topological phase transitions" induced by chemical doping. The goal of this project is to identify and to control native and/or extrinsic point defects in layered chalcogenide topological insulators such as Bi2Se3 and Sb2Te3. In addition, this project aims to achieve a comprehensive understanding of the mechanism of emergent multiple stripe modulations in the heavy di-chalcogenide IrTe2 which is closely related to devil's staircase phenomena due to competing interactions. Atomic-scale defects, electronic modulations and nanoscale inhomogeneity in these materials are visualized and examined using state-of-the-art scanning tunneling microscopy and spectroscopy. These research efforts are complimented by bulk probes, first-principle calculations and theoretical modeling via domestic and international collaborations.