# Overcoming limits to near-field radiative heat transfer in uniform planar media through multilayer optimization

## TL;DR

This paper demonstrates that multilayer geometries can surpass traditional limits of near-field radiative heat transfer in uniform plates by optimizing scattering and coupling of slab resonances, significantly enhancing flux in certain configurations.

## Contribution

It introduces a multilayer optimization approach to overcome fundamental limits in near-field radiative heat transfer between uniform media.

## Key findings

- Multilayer geometries can significantly increase radiative flux beyond traditional bounds.
- Enhanced flux is especially notable between a dipolar particle and an inhomogeneous slab.
- Hyperbolic metamaterials offer less enhancement compared to optimized inhomogeneous slabs.

## Abstract

Radiative heat transfer between uniform plates is bounded by the narrow range and limited contribution of surface waves. Using a combination of analytical calculations and numerical gradient-based optimization, we show that such a limitation can be overcome in complicated multilayer geometries, allowing the scattering and coupling rates of slab resonances to be altered over a broad range of evanescent wavevectors. We conclude that while the radiative flux between two inhomogeneous slabs can only be weakly enhanced, the flux between a dipolar particle and an inhomogeneous slab---proportional to the local density of states---can be orders of magnitude larger, albeit at the expense of increased frequency selectivity. A brief discussion of hyperbolic metamaterials shows that they provide far less enhancement than optimized inhomogeneous slabs.