Ultrabroadband THz probing of anisotropic optical conductivity and plasmonic damping in graphene nanostructures

Graphene nanostructures have garnered significant attention in the terahertz (THz) range due to their exceptional plasmonic properties. Exploring the THz conductivity of graphene nanostructures is crucial for optimizing their performance in advanced devices, necessitating comprehensive research into their optical responses across a broad frequency spectrum. In this study, we experimentally investigate the optical conductivity of graphene nanostructures using ultra-broadband THz time-domain spectroscopy. Extracted from the time-dependent THz echo signals, an order-of-magnitude enhancement of localized surface plasmon resonances (LSPRs) in graphene nanostructures was observed. This led to the anisotropic behavior in optical conductivity over the broadband THz range. In addition, the analyzed results show that LSPRs in graphene nanostructures experience damping loss from the intraband transition, resulting in energy dissipation into the substrate through the dielectric space layer. The induced redshift of the LSPR and linewidth broadening, in turn, modifies the optical conductivity of the graphene nanostructures. These findings provide valuable insights for developing advanced tunable THz devices based on graphene nanostructures.