Scientists Observe Valley-Polarized Plasmonic Edge Waves in the Near-Infrared
A research team has successfully visualized a valley-polarized plasmonic edge mode — a special type of light-matter wave that travels along the boundary of a nanostructured plasmonic crystal — in the near-infrared spectral range. “Valley polarization” refers to using distinct momentum valleys in a material’s electronic structure to encode wave propagation, a concept promising for robust waveguiding and information transfer. Until now, realizing such valley-polarized plasmon waves in metals was difficult due to energy losses. The team engineered a gap surface plasmon crystal with a wide bandgap that supports these waves and used cathodoluminescence in a scanning transmission electron microscope (STEM) to directly image their field distributions. They observed edge waves propagating over ~5.3 µm at energies of 1.31–1.36 eV, demonstrating a practical platform for nanoscale control of angular momentum between light (photons) and electronic carriers. This work bridges concepts from topological photonics and plasmonics and points toward new ways to manipulate light at deep sub-wavelength scales.

Journal: Nano Letters
DOI: 10.1021/acs.nanolett.1c01841