Multilayer Graphene Terahertz Plasmonic Structures for Enhanced Frequency Tuning Range

Graphene plasmonics has recently found a variety of applications in terahertz photonic devices. High spatial confinement and large frequency tunability are two key advantages of graphene plasmonics. Nevertheless, the frequency tuning range of plasmonic devices employing single-layer graphene is ultimately limited by its carrier density tuning range. Here, we demonstrate that the frequency tuning range of graphene-based plasmonic devices can be further extended by employing multilayer graphene structures. Both our experimental investigations and theoretical calculations show that the frequency tuning range of gate-controlled graphene plasmonic resonators can be significantly enhanced by employing two or three layers of stacked graphene, which is a result of the carrier distributions in multiple layers leading to higher total optical conductivity. However, contrary to the previous prediction, stacking even more graphene layers yields little additional benefit, as the interlayer charge screening effect leads to insignificant gate-induced carrier density in additional graphene layers. Our findings provide new insights for designing and optimizing graphene-based plasmonic structures for various photonic device applications, such as modulators, sensors, and detectors.