Topological plasmonic waveguides in triharmonic metal gratings

Area of Science:

• Condensed matter physics
• Plasmonics
• Topological photonics

Background:

• Surface-plasmon-polaritons (SPPs) are crucial for light manipulation at the nanoscale.
• Topological concepts offer robust protection against disorder in various physical systems.
• Diffraction gratings provide a versatile platform for controlling electromagnetic waves.

Purpose of the Study:

• To investigate topological surface-plasmon-polaritons at optical frequencies.
• To explore the realization of topological states in tri-harmonic diffraction gratings.
• To analyze the behavior of localized modes at grating edges and defects.

Main Methods:

• Modeling tri-harmonic diffraction gratings at a metal-dielectric interface.
• Approximating the grating system with a bipartite Kronig-Penney model.
• Calculating the bulk invariant (Zak phase) to predict topological properties.

Main Results:

• Tri-harmonic gratings effectively mimic a bipartite Kronig-Penney model.
• Topologically protected localized modes are predicted at grating edges and specific defects.
• A step-wise varying Zak phase characterizes the bulk invariant for these topological states.
• A special case reveals forbidden defect states, highlighting potential fragility.

Conclusions:

• Topological surface-plasmon-polaritons can be realized in engineered diffraction gratings.
• Localized modes at edges and defects exhibit topological protection.
• The Zak phase serves as a key indicator for topological properties in this system.
• The fragility of certain topological defect states warrants further investigation.