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移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，并且运动是未知的。 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。 了解运动可以生产出阻力更小、导热性更好的材料，并且可以以比当前方法成本更低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，用于理解材料的物理特性，学生使用触觉模型和触觉反馈系统来“感觉”材料的晶格，就像电子或分子一样。 这些课程正在为高级本科实验室和K-12推广计划开发，旨在以直观和难忘的方式解释材料的特性。 此外，还为老年人和视力不同的人开发了一个旅行课程，这样他们就可以以一种吸引人的触觉方式学习材料;威斯康星州大学的祖父母大学正在开发一个课程，老年人和他们的孙辈一起学习科学概念。技术摘要：该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）-分别对材料中的纳米级电荷和热量流动进行成像，例如石墨烯，具有流体动力学和量子霍尔相。 流体动力学材料系统表现出违反Wiedemann-Franz定律的新的热电性质，并且已经被预测为显示涡旋甚至湍流的电子和热流。 在该项目中使用组合STP和STST测量来确定在这种系统中热量和电荷流变得不相关的程度，并且该项目还利用了不同地影响热量和电荷流的工程势垒，目的是进一步解耦两者。 此外，通过探测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学材料中自洽地解决热电流的完整问题的数据。 STP测量磁场中的电荷运动，同时，探索如何弱束缚态和蛇态可以扰动量子霍尔电导平台的值，并沉淀形成的漩涡循环流动的电荷作为系统的粘度增加。 这些测量也验证了电子粘性本身在量子霍尔系统中应该量子化的预测。 该项目对从流体动力学材料中改进热电设备以及理解流体动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NSF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.