Optical Study of Electron Correlation in Graphene-Based Moire Superlattices

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Non-technical description:Superlattices, stacks of multiple layers of materials with different compositions, formed from two-dimensional (2D) materials host incredible flexibilities in engineering material properties through controlling the stacking order, the twist angle, and tuning of the electron density. Such engineered materials have remarkable electrical and optical properties that do not exist in individual 2D materials. This project advances our understanding of carbon-based materials, thus enabling new design principles of quantum materials and their device applications for quantum science and technology. This project helps graduate and undergraduate students from under-represented groups bridge the gap between textbook learning and scientific research by providing interdisciplinary scientific experience. It stimulates the interest of K-12 students in 2D materials and the fields of science, technology, engineering, and mathematics, training the future workforce. This project also enriches the experimental capabilities of the user facility at the NSF-funded National High Magnetic Field Laboratory and provides technical support to users in the broad quantum materials research community.Technical description:This project address fundamental questions regarding electron correlation in the moiré superlattices involving few-layer graphene and hexagonal boron nitride. The research team uses this new material platform to engineer and study superconductivity, Mott insulator, and magnetic ground states— physics that were previously realized in conventional strongly correlated materials such as high-Tc superconductors. The proposed research advances the field of 2D materials through the following innovations. (1) It generates the first infrared spectroscopy data of several graphene-based moiré superlattices and reveals critical energy scales relevant to electron correlation. Such information forms the basis of accurate theoretical modeling and better interpretation of already discovered correlation phenomena. (2) It develops unique optical spectroscopy and microscopy tools that help fabricate new device structures with widely tunable twist angle, charge density and band structures. By performing electron transport measurement on these devices, the research team explores the limit of electron correlation such as the superconducting transition temperature Tc. (3) It systematically studies the connection and difference between correlation phenomena in moiré and non-moiré systems of 2D materials. This helps understand the exact role of moiré superlattice for better engineering of electron correlation in stacks of 2D materials.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.