Nonlocal response in plasmonic waveguiding with extreme light confinement

TL;DR

This paper introduces a new wave equation for plasmonic response that fully incorporates nonlocal effects, enabling the study of ultra-confined waveguides and revealing fundamental limits on light confinement and Purcell factors.

Contribution

A novel nonlocal wave equation for plasmonic response that improves numerical modeling of ultra-confined waveguides and reveals fundamental confinement limits.

Findings

Groove and wedge waveguides have a fundamental lower limit in mode confinement.

Nonlocal effects set an upper limit on Purcell factors.

Extreme light confinement is limited by nonlocal dynamics.

Abstract

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.