CAREER: Revealing the Dynamics of Charge Carriers in Strongly Correlated Materials with Scanning Tunneling Potentiometry

非技术摘要：电子和热量在材料中的运动方式通常被认为类似于台球或扩散扩散，但在许多材料中并非如此，运动是未知的。该项目旨在开发新的显微镜技术，可用于在微观水平上直接可视化材料中的电子和热量流动。了解运动可以使材料产生更小的阻力，更好的导热性，并且可以以比当前方法更便宜的方式模拟流体和空气流动。该项目的一个重要方面是开发基于触摸的学习工具，以理解材料的物理特性，学生使用触觉模型和触觉反馈系统以与电子或分子相同的方式“感受”材料的晶格。这些课程是为高级本科实验室和K-12推广项目开发的，目的是以直观和难忘的方式解释材料的特性。还为老年人和视力不同的人开设了一个旅行班，使他们能够以一种吸引人的触觉方式学习材料；以及为威斯康星大学的祖父母大学（Grandparents University）开设的一门课程，让老年人和他们的孙子一起学习科学概念。技术摘要：本项目旨在推进和利用两种扫描探针技术-扫描隧道电位法（STP）和扫描隧道超导测温法(STST) -分别成像具有流体动力和量子霍尔相的材料（如石墨烯）中的纳米级电荷和热量流动。流体动力材料系统表现出违反Wiedemann-Franz定律的新型热电性质，并被预测为显示涡旋甚至湍流的电子和热流。在这个项目中，结合STP和STST测量来确定热流和电荷流在这样的系统中变得不相关的程度，并且这个项目还利用了影响热流和电荷流的工程势垒，目的是进一步解耦两者。此外，通过探索热如何在粘性电子相中消散，该项目探索了限制这些相的导电性的机制，并提供了允许在流体动力材料中自一致地解决热电流动完整问题的数据。同时，STP测量磁场中的电荷运动，探索弱束缚态和蛇形态如何随着系统粘度的增加而扰动量子霍尔电导平台的值，并促使循环流动电荷涡旋的形成。这些测量也验证了电子粘度本身在量子霍尔系统中应该量子化的预测。该项目对于利用流体力学材料制造改进的热电器件，以及理解流体力学对其他材料系统的影响具有广泛的意义。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。

Non-technical abstract: The way in which electrons and heat move through a material is often assumed to resemble billiard balls or diffusive spreading, but in many materials this is not the case and the movement is unknown. This project aims to develop new microscopy techniques that can be used to directly visualize the flow of electrons and heat in a material at the microscopic level. Understanding that motion allows materials to be produced that have less resistance, better heat conductivity, and that can model fluid and air flows in ways that are less costly than current methods. A significant aspect of this project is to develop touch-based learning tools for understanding the physics of materials, where students use tactile models and haptic-feedback systems to ‘feel’ the crystal lattice of a material in the same way an electron or molecule would. These lessons are being developed for advanced undergraduate labs and for K-12 outreach programs, with an aim of explaining the properties of materials in an intuitive and memorable way. A travelling class is also being developed for older adults and differently sighted individuals, so that they can learn about materials in an engaging tactile manner; and a class in being developed for Grandparents University at the University of Wisconsin, where older adults and their grandchildren learn about scientific concepts together.Technical abstract: This project aims to advance and utilize two scanned probe techniques – scanning tunneling potentiometry (STP) and scanning tunneling superconducting thermometry (STST) – to separately image the nanoscale flow of charge and heat in materials, such as graphene, with hydrodynamic and quantum hall phases. Hydrodynamic material systems exhibit novel thermoelectric properties that violate the Wiedemann-Franz law, and have been predicted to display vortical or even turbulent electron and heat flow. Combined STP and STST measurements are used in this project to determine the degree to which heat and charge flow becomes uncorrelated in such systems, and this project also utilizes engineered potential barriers that affect heat and charge flow differently, with an aim of further decoupling the two. Moreover, by probing how heat is dissipated in viscous electronic phases, this project explores the mechanisms that limit the conductivity of such phases and provides data that allows the complete problem of thermoelectric flow to be solved self-consistently in hydrodynamic materials. STP measurements of charge motion in magnetic fields, meanwhile, explore how weakly bound states and snake states can perturb the values of quantum hall conductance plateaus and precipitate the formation of vorticies of circularly flowing charge as the viscosity of the system is increased. These measurements also test predictions that electron viscosity itself should become quantized in quantum hall systems. This project has broad implications for creating improved thermoelectric devices from hydrodynamic materials, and for understanding the effect of hydrodynamics on other material systems.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.