Nonlocality in metallo-dielectric multilayers: numerical tools and physical analysis

TL;DR

This paper develops theoretical and numerical tools to analyze how nonlocal electron effects influence the optical properties of thin metallo-dielectric multilayers, especially in structures with flat dispersion curves, revealing increased transmission and significant effects on gap-plasmon resonances.

Contribution

It introduces a hydrodynamic model-based approach to quantify nonlocal effects in multilayers, highlighting their impact on transmission and plasmon resonances.

Findings

Nonlocal effects slightly increase transmission in thin metallic layers.

Nonlocality significantly influences gap-plasmon resonances.

Tools enable better understanding of nonlocality in advanced optical materials.

Abstract

We provide theoretical and numerical tools to quantitatively study the impact of nonlocality arising from free electrons in metals on the optical properties of metallo-dielectric multilayers. Though effects due to nonlocality are in general quite small, they nevertheless can be important for very thin (typically below 10 nm) metallic layers - as are used in structures characterized by relatively flat dispersion curves. Such structures include those with negative refractive index; hyperbolic metamaterials; and materials with index near zero. We find in all cases that the inclusion of nonlocal effects through application of the hydrodynamic model to the electron response leads to a higher transmission through the considered medium. Finally, we examine the excitation of gap-plasmon resonances, where nonlocality plays a much greater role, and suggest possible routes for experimental investigation.