Hidden Symmetry Protection and Topology in Surface Maxwell Waves

TL;DR

This paper reveals the hidden symmetry protection behind surface plasmon polaritons, linking topological concepts to their physical origins and demonstrating their robustness through a bulk-edge correspondence in surface impedance.

Contribution

It uncovers the hidden symmetry protection mechanism of surface waves, identifies zero modes as their physical origin, and establishes a topological framework for understanding surface plasmon polaritons.

Findings

Zero modes are the physical origin of surface plasmon polaritons.

Bulk-edge correspondence guarantees surface waves even with nonuniformity.

Topological transition between metal and dielectric involves crossover of electric and magnetic zero modes.

Abstract

Since the latter half of the 20th century, the use of metal in optics has become a promising plasmonics field for controlling light at a deep subwavelength scale. Surface plasmon polaritons localized on metal surfaces are crucial in plasmonics. However, despite the long history of plasmonics, the underlying mechanism producing the surface waves is not fully understood. This study unveils the hidden symmetry protection that ensures the existence of degenerated electric zero modes. These zero modes are identified as physical origins of surface plasmon polaritons, and similar zero modes can be directly excited at a temporal boundary. In real space, the zero modes possess vector-field rotation related to surface impedance. Focusing on the surface impedance, we prove the bulk-edge correspondence, which guarantees the existence of surface plasmon polaritons even with nonuniformity. Lastly, we extract the underlying physics in the topological transition between metal and dielectric material using a minimal circuit model with duality. The transition is considered the crossover between electric and magnetic zero modes.