Near-field imaging of synthetic dimensional integrated plasmonic topological Harper nanochains.

Topological photonics offers immense potential for applications in integrated photonic devices and information processing chips. Aubry-André-Harper model provides a platform for exploring new physics and practical applications. However, the on-chip integration of an ultracompact Aubry-André-Harper plasmonic topological insulator has encountered two limitations: the strict precision requirements for coupling parameters during sample preparation and the presence of hotspots in the nanogaps between plasmonic nanostructures, which impede direct near-field measurements. In this work, we propose a novel approach to address these challenges by integrating gold nanodisks with connecting waveguides. The topological properties of the Aubry-André-Harper configuration are directly characterized using photoemission electron microscopy. Connecting gold nanodisks with short gold waveguides of varying widths ensures compliance with the stringent precision requirements for sample nanofabrication and minimizes the impact of plasmon hotspots. We also successfully excite nanodisks in odd or even positions of trivial staggered nanochains by using incident left- or right-circularly polarized light. This approach effectively enables polarization-multiplexing control, offering a promising method for further manipulating and refining plasmonic nanochains and their potential applications. This work provides direct in-situ measurements of topological states at the nanoscale, advancing the foundational research and practical applications of controlling synthetic dimensions in integrated plasmonic topological photonics.