Atomic-scale Imaging of Novel Electronic States in Kagome Superconductors

非技术摘要：所谓的Kagome材料结构的特征是原子排列在共享角落的三角形的角落中。这种结构已经成为研究新奇现象的丰富平台。由于Kagome结构的几何形状，这些系统中的电子可以具有其他材料中很少找到的明显特征。然而，Kagome系统的基本物理性质在根本层面上仍然知之甚少。该项目旨在了解一种新的Kagome材料家族的奇异特性。为了做到这一点，研究人员使用了扫描隧道显微镜和光谱学的现代实验方法。该项目的重点是研究磁场、应变和化学成分变化对这些系统性能的影响。这项研究旨在加深对Kagome材料的基本了解，并为其最终在技术上的使用和应用奠定基础。综合研究和教育活动旨在通过在当地学校建立外联活动和提供实验室参观来培训和教育学生。为了激励年轻学生追求科学事业，PI为高中生和他实验室中代表性不足的群体提供研究机会。技术摘要：过渡金属原子的Kagome晶格提供了一个在几何受挫和非平凡能带拓扑存在的情况下研究电子关联的令人兴奋的平台。最近发现的一类层状Kagome金属AV3Sb5(A=K，Cs或Rb)，由钒原子组成的Kagome网络组成，引起了社区的极大兴趣。人们已经提出了大量有趣的理论和实验现象，例如观察到异常的霍尔响应，各种密度波，以及在Kagome系统中罕见的超导现象。本项目的重点是使用变温光谱成像扫描隧道显微镜来探索这类新材料中的新电子现象。具体地说，它的目标是：(1)揭示这些材料中电子向列相的存在，(2)揭示令人惊讶的电荷条纹相的光谱起源，(3)提供对观察到的密度波和超导电性如何随着化学掺杂、温度和应变的变化而演变的全面的原子尺度的见解，(4)确定磁场对电子能带结构的影响，以寻找轨道矩的特征，以及(5)揭示超导的性质和沿着磁区壁传播的一维模的存在。原位矢量磁铁和光谱成像扫描隧道显微镜的结合为直接绘制作为矢量磁场函数的能带结构提供了一种难得的工具。PI的综合研究和教育活动旨在通过在当地初中和高中建立外联活动并提供实验室参观来影响广泛的学生。为了激励年轻学生追求科学事业，PI为高中生和他实验室中未被充分代表的群体提供研究机会。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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 so-called kagome material structure is characterized by the arrangement of atoms residing in the corners of corner-sharing triangles. This structure has emerged as a rich platform to study novel phenomena. Due to the geometry of the kagome structure, electrons in these systems can have distinct characteristics that are rarely found in other materials. However, the underlying physical properties of kagome systems are still poorly understood at a fundamental level. This project aims to understand the exotic properties of a new family of kagome materials. To accomplish this, the researchers employ modern experimental methods of scanning tunneling microscopy and spectroscopy. The project focuses on studying the effects of magnetic field, strain, and chemical composition change on the properties of these systems. The research aims to deepen the fundamental understanding of kagome materials, and establish the foundation for their eventual use and applications in technology. Integrated research and education activities aim to train and educate students via establishing outreach events in local schools, and by giving lab tours. To motivate young students to pursue science careers, the PI provides research opportunities for high-school students and underrepresented groups in his lab. Technical abstract: The kagome lattice of transition metal atoms offers an exciting platform to study electronic correlations in the presence of geometric frustration and nontrivial band topology. The recently discovered class of layered kagome metals AV3Sb5 (A=K, Cs or Rb), composed of a kagome net of Vanadium atoms, has generated significant interest in the community. There has been an avalanche of intriguing theories proposed and experimental phenomena observed, for example the observation of anomalous Hall response, various density waves, and a rare occurrence of superconductivity in a kagome system. This project focuses on using variable-temperature spectroscopic-imaging scanning tunneling microscopy to explore novel electronic phenomena in this new class of materials. Specifically, it aims to: (1) reveal the existence of electronic nematic phase in these materials, (2) uncover what is the spectroscopic origin of the surprising charge stripe phase, (3) provide a comprehensive atomic-scale insight into how the observed density waves and superconductivity evolve as a function of chemical doping, temperature and strain, (4) determine the effect of magnetic field on the electronic band structure to look for signatures of orbital moments, and (5) shed light on the nature of superconductivity and the existence of one-dimensional modes propagating along domain walls. The combination of in situ vector magnet and spectroscopic-imaging scanning tunneling microscopy provides a rare tool for direct band structure mapping as a function of vector magnetic field. The PI’s integrated research and education activities aim to impact a wide range of students via establishing outreach events in local middle and high schools, and giving lab tours. To motivate young students to pursue science careers, the PI provides research opportunities for high-school students and underrepresented groups in his lab.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.