Collaborative Research: Probing quasiparticle excitations in TMDC Moiré superlattices for revealing and understanding novel two-dimensional correlated phases

非技术摘要：由于二维（2D）原子晶体的发展，研究人员已经成功地创造了一种新的周期晶格，这种晶格是由两个垂直堆叠的二维原子晶格的干涉产生的。这种所谓的“云纹超晶格”的存在，已经被理论预测和实验证明。在这个合作项目中，研究小组研究了一类由过渡金属二硫族化物（TMDC）制成的云纹超晶格。该团队旨在通过探测这些TMDC堆叠结构中的周期性晶格、载流子和磁矩的动力学，了解半导体TMDC单层如何在垂直堆叠在一起时变成非常规绝缘体、磁铁甚至超导体的关键问题。该项目进一步与教育和外展活动相结合，以招募和指导代表性不足的第一代学生，向K-12学生展示演示实验和教程，并向公众介绍合作研究的背景和结果。这些活动涉及广泛的参与者群体，并在K-12学生和公众中推广科学、技术和工程。技术摘要：通过实验证明，两个原子薄晶体之间的晶格失配或角不对中形成的云纹超晶格是设计和工程二维系统电子特性的有效方法。一个特别突出的例子是小扭角TMDC云纹超晶格，显示出丰富的强相关电子相，而这些电子相在单个组成TMDC单层中是不存在的。在这个合作项目中，研究目标是全面了解TMDC云纹超晶格中出现的相关相。重点是利用综合光谱学实验和第一性原理理论方法研究这些相关相的声子、电荷和磁振子的集体激发。具体而言，研究小组制作了TMDC云纹超晶格，利用时间分辨和拉曼光谱进行时域和频域动态测量，并进行理论计算来指导实验设计和解释实验结果。该项目的成功不仅为更好地理解二维系统中的新兴相关物理开辟了新的途径，而且为探索一般的强相关物理扩展了平台。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:Thanks to the development of two-dimensional (2D) atomic crystals, researchers have managed to create a new kind of periodic lattice that arises from the interference of two vertically stacked 2D atomic lattices. The existence of this so called "moire superlattice", has been theoretically predicted and experimentally demonstrated. In this collaborative project, the research team studies a family of such moire superlattices made from transition metal dichalcogenides (TMDC). The team aims at understanding the key questions of how semiconducting TMDC monolayers turn into unconventional insulators, magnets, or even superconductors when stacked together vertically, by probing the dynamics of the periodic lattices, the charge carriers, and the magnetic moments in these TMDC stacked structures. The project is further integrated with education and outreach activities to recruit and mentor underrepresented and first-generation students, present demo experiments and tutorials to K-12 students, and introduce the background and results from collaborative research to the general public. These activities involve a wide group of participants and promote science, technology, and engineering among K-12 students and the public.Technical abstract:The formation of moire superlattice by either lattice mismatch or angular misalignment between two atomically thin crystals has been experimentally demonstrated as a powerful way to design and engineer electronic properties of 2D systems. One particular outstanding example is the small twist-angle TMDC moire superlattices, showing a wealth of strongly correlated electronic phases that are absent in the individual composing TMDC monolayers. In this collaborative project, the research goal is to develop a comprehensive understanding on these emergent correlated phases in TMDC moire superlattices. The focus is to investigate the collective phonon, charge, and magnon excitations of these correlated phases by using an integrated optical spectroscopy experiment and first-principles theory method. Specifically, the research team fabricates TMDC moire superlattices, performs time- and frequency-domain dynamic measurements using time-resolved and Raman optical spectroscopy, and carries out theoretical calculations to guide the experimental design and interpret the experimental results. The success of this project not only opens a new pathway to better understand emergent correlated physics in 2D systems, but also expands the platform to explore strongly correlated physics in general.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.