Visualizing quantum Hall ferromagnets, their 1D topological edge modes and their interplay with superconductivity

拓扑相位的研究与量子场论中的概念和建立容错量子计算机的方法都有联系。凝聚态系统中的低能、涌现准粒子可以提供一个实验室来测试场论概念，这一想法遵循了将物理学中的概念推广到能量和长度尺度的悠久传统。与拓扑材料的研究同样重要的是，拓扑相和相关的涌现准粒子很可能为电子学提供基本的新方法。例如，固体中电子波函数的谷自由度（valley degree of freedom）是一个被提出来用于制造新型电子器件的特性。在这个项目上培训的研究生和本科生正在学习最先进的扫描探针显微镜，低温学和材料物理实验技术，这些技术对工业界和学术界都有浓厚的兴趣。随着普林斯顿大学新生研讨会课程的发展，实验室研究正在进入课堂，向学生介绍量子力学，量子计算的一些基础知识，并将他们暴露在量子凝聚态物理学的“桌面”发现中，如超导性，超流性，激光冷却和玻色凝聚。该课程旨在向那些受过最少培训的人介绍量子现象，本项目是一个以科学和数学为基础的高中课程。这种方法将使来自不同学术背景和兴趣的学生在他们的职业生涯早期就接触到凝聚态物理和量子现象的兴奋。技术摘要本项目的重点是研究电子相，其中电子和它们的拓扑结构之间的相互作用。波函数必须同等对待。这些是量子霍尔铁磁相，其中电子的谷自由度使得拓扑量子霍尔态也显示出由电子之间的交换相互作用驱动的对称性破缺。为了实现其目标，该计划带来了高能量和空间分辨率光谱映射与扫描隧道显微镜（STM）的力量，不仅可视化谷量子霍尔铁磁体在真实的空间，而且还探测其拓扑边界模式，并通过改变其载流子密度，或使用应变，以及接近超导体和磁体来调整其属性。一类新的相互作用的一维Luttinger液体，形成在不同的量子霍尔谷阶段之间的拓扑边界检查在此程序。 此外，该计划还探索了在低载流子浓度下相互作用的物理学，以在STM可访问的电子系统（Bi和其他表面状态）中驱动条纹，气泡或分数量子霍尔相位，并首次可视化这些相位。研究了量子霍尔谷极化相与特殊混合结构中超导性的相互作用。这些努力将探索当来自传统超导体的涡旋晶格与具有强自旋轨道耦合的二维（2D）电子气在量子化朗道能级（LL）的存在下耦合时，Majoranas的“晶格”和拓扑超导性可能出现的方式。一些不同的材料将被探索，以扩大我们的能力，可视化朗道波函数到其他二维系统。该计划将汇集广泛的实验，材料和薄膜结构的新颖创造，以实现拓扑电子相和相关的新现象，可以使用STM直接研究高空间和能量分辨率。这项研究是由首席研究员和他的研究团队设计和建造的高分辨率STM仪器实现的。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 AbstractResearch on topological phases has connection to both concepts in quantum field theory and proposed approaches for creation of fault tolerant quantum computers. The idea that low energy, emergent quasiparticles in condensed matter systems can provide a laboratory to test field theory concepts follows the long tradition of generalizing concepts in physics across energy and length scales. Equally important to the study of topological materials, topological phases and associated emergent quasiparticles may well provide fundamental new approaches to electronics. For example, valley degree of freedom for electronic wavefunction in solids, a property examined here, is a feature that has been proposed to create new types of electronic devices. The graduate and undergraduate students trained on this project are learning state-of-the-art scanning probe microscopy, cryogenics, and materials physics experimental techniques that are of strong interest to both industry and academia. Lab research is being moved into the classroom with the development of a Princeton freshman seminar course introducing students to some basics of quantum mechanics, quantum computing, and exposing them to 'tabletop' discoveries in quantum condensed matter physics such as superconductivity, superfluidity, laser cooling and Bose condensation. The course is designed to introduce quantum phenomena to those with minimal training, with only high school courses in science and math. This approach will allow students from various academic backgrounds and interests to be exposed to the excitement of condensed matter physics and quantum phenomena early in their career.Technical AbstractThis project is focused on the study of electronic phases in which interaction between electrons and topology of their wavefunctions must be treated on equal footing. These are quantum Hall ferromagnetic phases in which electrons' valley degree of freedom makes the topological quantum Hall states also display broken symmetry driven by the exchange interaction between electrons. To accomplish its goals, the program brings the power of high energy and spatial resolution spectroscopic mapping with a scanning tunneling microscope (STM) to not only visualize valley quantum Hall ferromagnets in real space, but also to probe their topological boundary modes and to tune their properties by changing their carrier density, or using strain, and proximity with superconductors and magnets. A new class of interacting 1D Luttinger liquids that form at the topological boundary between different quantum Hall valley phases is examined during this program. In addition, the program explores the physics of interactions at low carrier concentrations to drive stripe, bubble, or fractional quantum Hall phases in an electronic system (Bi and other surface states) accessible to STM, and visualize these phases for the first time. The interplay between quantum Hall valley-polarized phases with superconductivity in special hybrid structures are also studied. These efforts will explore ways in which Majoranas' "lattices" and topological superconductivity may emerge when a vortex lattice from a conventional superconductor is coupled with a two-dimensional (2D) electron gas with strong spin-orbit coupling in the presence of a quantized Landau level (LL). A number of different materials will be explored to extend our ability to visualize Landau wavefunction to other 2D systems. The program will bring together a wide range of experiments, novel creation of materials and thin film structures to realize topological electronic phases and associated novel phenomena that can be directly studied with high spatial and energy resolution using the STM. The research is made possible by high-resolution STM instrumentation that have been designed and constructed by the principal investigator and his research team.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.