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建了一种新的周期性晶格，这种晶格是由两个垂直堆叠的2D原子晶格的干涉产生的。这种所谓的“莫尔超晶格”的存在，已被理论预测和实验证明。在这个合作项目中，研究小组研究了由过渡金属二硫属化物（TMDC）制成的一系列这样的莫尔超晶格。该团队的目标是了解半导体TMDC单层如何在垂直堆叠在一起时变成非常规绝缘体，磁体甚至超导体的关键问题，通过探测这些TMDC堆叠结构中的周期性晶格，电荷载流子和磁矩的动力学。该项目进一步与教育和外联活动相结合，以招募和指导代表性不足的第一代学生，向K-12学生提供演示实验和教程，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，并促进K-12学生和公众之间的科学，技术和工程。技术摘要：无论是晶格失配或两个原子级薄晶体之间的角度错位形成的莫尔超晶格已被实验证明是一个强大的方式来设计和工程的二维系统的电子性能。一个特别突出的例子是小扭曲角TMDC莫尔超晶格，显示了丰富的强烈相关的电子相，是在个别组成TMDC单层缺席。在这个合作项目中，研究目标是对TMDC莫尔超晶格中这些涌现的相关相有一个全面的了解。重点是研究集体声子，电荷和磁振子激发这些关联相通过使用集成的光谱实验和第一性原理理论方法。具体而言，研究团队制作TMDC莫尔超晶格，使用时间分辨和拉曼光谱进行时域和频域动态测量，并进行理论计算以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2D系统中的涌现相关物理开辟了新途径，而且还扩展了探索强相关物理的平台。该奖项反映了NSF的法定使命，并通过使用基金会的智力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.