"Plasmon worldlines: Unveiling Electronic correlations and geometry in Quantum materials"
The intricate interplay between electronic correlations and quantum geometry gives rise to various exotic phases of matter. Plasmons, the quanta of charge density oscillations in electron liquids, are typically unaffected by interactions and well described by classical electromagnetism. However, we demonstrate that plasmon dynamics in 2D materials can be strongly renormalized due to electron-electron interactions and quantum geometrical effect. Using nano-terahertz Spacetime metrology(1), we experimentally study plasmons in monolayer and bilayer graphene at sub-terahertz frequencies, recording their worldlines directly in spacetime. In monolayer graphene, we observed significant deviations from the predictions of Fermi-liquid theory, particularly when electron and hole densities are nearly equal. These deviations manifest as enhanced plasmon damping due to strong electron-hole interactions. In Bernal bilayer graphene, the Galilean invariance is broken due to the momentum-dependent layer pseudospins—rooted in the quantum geometry of electron wave functions. This leads to massive correlation effects in plasmon dispersion, even in the long-wavelength limit. We found that the Drude weight is strongly enhanced as charge carrier density approaches zero, a result of the quantum metric blowing up at the center of the Brillouin zone. Our findings offer new insights into the role of spacetime symmetry, electronic correlations, and quantum geometry in the macroscopic collective response of quantum many-body systems.
1. S. Xu, Y. Li, R. A. Vitalone, R. Jing, A. J. Sternbach, S. Zhang, J. Ingham, M. Delor, J. W. McIver, M. Yankowitz, R. Queiroz, A. J. Millis, M. M. Fogler, C. R. Dean, J. Hone, M. Liu, D. N. Basov, Electronic interactions in Dirac fluids visualized by nano-terahertz spacetime mapping. arXiv, doi: 10.48550/arxiv.2311.11502 (2023).
