Doping Effects on Excited-State Properties of Two-Dimensional Moiré Crystals

Washington University, Saint Louis MO

Investigators

Abstract

NONTECHNICAL SUMMARY This award supports theoretical and computational research and educational activities that aim to advance the understanding of interactions between electrons in two-dimensional Moire crystals, which are emerging quantum materials formed by stacking two atomic layers with a twisting angle. These twisted structures render a periodic potential that confine electrons and significantly enhance their interactions, giving rise to new electronic and optical properties, such as superconductivity, magnetism, metal/insulator transitions, and highly efficient optical absorption/emission. In this project, the PI plans to efficiently control this confinement effect by adding or extracting electrons from the crystal. Because of the unique two dimensionality of Moire crystals, the PI expects that a small variation in the number of electrons can dramatically tune the confinement potential and subsequently change the electrical conductance, magnetism, and light-matter interactions by orders of magnitude. To accurately calculate these unique electronic interactions, the PI will develop theoretical models and implement them in high-performance simulation packages. The predicted tunable many-electron interactions and electronic and optical properties can potentially lead to the realization of novel electronic devices, programable photon emitters/detectors, and dissipationless electronic states that are promising for energy-efficient quantum-information applications. In addition to the research efforts, this award also supports the training and education of graduate and undergraduate students as the next-generation scientific and engineering workforce. Female and minority students will be recruited to engage in exploring new properties and applications of quantum materials by large-scale simulations. The PI will also develop a simulation-based condensed matter physics course for undergraduate students. TECHNICAL SUMMARY This award supports an integrated research, education, and outreach program focusing on exploring doping dependent excited-state properties of two-dimensional Moire crystals. The periodic quantum confinement formed by Moire patterns is expected to trap quasiparticles and excitons and to realize arrays of identical quantum dots for programmable transport and optical applications. Moreover, these Moire potentials can enhance van Hove singularities and render unusual many-body physics, such as the Mott insulating phase, Wigner crystals, unconventional superconductivity, exciton condensation, and topological orders. All these desired phenomena and applications are essentially decided by quasiparticles and excitons, which are excited states formed by many-electron interactions. In this project, the PI will calculate the enhanced doping effects on many-electron screening and hence the excited states, functioning as an efficient means of tuning Moire potentials, many-body physics, and topological orders. The PI will develop first-principles many-body perturbation theory methods to capture the coupling between Moire plasmons and excited states for calculating quasiparticles and excitons in doped two-dimensional Moire materials. New opportunities to realize flat exciton bands and exciton insulators by doping narrow-gap topological Moire crystals will also be investigated. In addition to the research efforts, this award also supports the training and education of graduate and undergraduate students as the next-generation scientific and engineering workforce. Female and minority students will be recruited to engage in exploring new properties and applications of quantum materials by large-scale simulations. The PI will also develop a simulation-based condensed matter physics course for undergraduate students. 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.