1 Department of Photonics Engineering, Technical University of Denmark2 Structured Electromagnetic Materials, Department of Photonics Engineering, Technical University of Denmark3 Department of Micro- and Nanotechnology, Technical University of Denmark4 Theoretical Nanotechnology, Department of Micro- and Nanotechnology, Technical University of Denmark5 Center for Electron Nanoscopy, Technical University of Denmark6 Center for Nanostructured Graphene, Center, Technical University of Denmark
We present a novel wave equation for linearized plasmonic response, obtained by combining the coupled real-space differential equations for the electric field and current density. Nonlocal dynamics are fully accounted for, and the formulation is very well suited for numerical implementation, allowing us to study waveguides with subnanometer cross-sections exhibiting extreme light confinement. We show that groove and wedge waveguides have a fundamental lower limit in their mode confinement, only captured by the nonlocal theory. The limitation translates into an upper limit for the corresponding Purcell factors, and thus has important implications for quantum plasmonics.