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

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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.