Fluctuational electrodynamics of hyperbolic metamaterials

TL;DR

This paper explores the fluctuational electrodynamics of hyperbolic metamaterials, unifying different theoretical approaches, analyzing near-field thermal emission, and identifying regimes for experimental validation in thermal photonics.

Contribution

It provides a comprehensive analysis of equilibrium and non-equilibrium fluctuations in hyperbolic metamaterials, unifying two theoretical frameworks and applying them to phonon-polaritonic super-lattice structures.

Findings

Multi-modal super-Planckian thermal emission causes lack of spatial coherence.

Far-field emission spectra are dominated by epsilon-near-zero and epsilon-near-pole responses.

Identifies regimes suitable for experimental verification of fluctuation effects.

Abstract

We give a detailed account of equilibrium and non-equilibrium fluctuational electrodynamics of hyperbolic metamaterials. We show the unifying aspects of two different approaches; one utilizes the second kind of fluctuation dissipation theorem and the other makes use of the scattering method. We analyze the near-field of hyperbolic media at finite temperatures and show that the lack of spatial coherence can be attributed to the multi-modal nature of super-Planckian thermal emission. We also adopt the analysis to phonon-polaritonic super-lattice metamaterials and describe the regimes suitable for experimental verification of our predicted effects. The results reveal that far-field thermal emission spectra are dominated by epsilon-near-zero and epsilon-near-pole responses as expected from Kirchoff's laws. Our work should aid both theorists and experimentalists to study complex media and engineer equilibrium and non-equilibrium fluctuations for applications in thermal photonics.