Abstract
Polaritons—hybrid light–matter excitations—in 2D materials provide unique opportunities for controlling light at nanoscales. Tailoring these excitations via gradient polaritonic surfaces with space-variant optical response can enable versatile light–matter interaction platforms with completely new phenomena and advanced functionalities. Here we report a natural class of gradient polaritonic surfaces based on superlattices of domain wall solitons in 2D moiré systems. In twisted bilayer graphene on boron nitride, we demonstrate on-off switching and continuous tuning of local polariton-soliton interactions with a critical yet unexplored degree of freedom—the soliton angle that characterizes the local strain direction. We show that such tunability arises from dramatic modifications of topological as well as conventional soliton states by local soliton angle. Furthermore, we reveal the capability of these structures to spatially modify the near-field profile, phase and propagation direction of polaritons in record small footprints, enabling generation and electrical switching of directional polaritons. Our results unlock the enormous potential of 2D moiré materials to serve as gradient polaritonic surfaces with spatially tailored light-matter interactions, opening up new avenues for nanoscale spatial polariton engineering and for exploring novel photonic physics in moiré soliton superlattices.
Biosketch
Zhiqiang Li is a professor at College of Physics, Sichuan University. He earned his PhD in Physics from University of California, San Diego in 2008, followed by a postdoc position at Columbia University and research faculty at National High Magnetic Field Lab, USA. His research area is experimental condensed matter physics, focusing on optical and electronic properties of low-dimensional systems and topological materials, such as graphene and other novel 2D materials, topological insulators, etc.
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