# Fundamental limits to radiative heat transfer: the limited role of nanostructuring in the near field

## TL;DR

This paper establishes fundamental limits on near-field radiative heat transfer, showing nanostructuring cannot surpass these bounds, especially for extended structures, due to multiple scattering effects.

## Contribution

It applies algebraic and fundamental principles to derive limits for different geometries, highlighting the limited role of nanostructuring in enhancing heat transfer.

## Key findings

- Near-field transfer between dipoles can reach geometric limits.
- Extended structures' transfer grows slowly with material response.
- Nanostructuring cannot surpass fundamental bounds due to multiple scattering.

## Abstract

In a complementary article, we exploited algebraic properties of Maxwell's equations and fundamental principles such as electromagnetic reciprocity and passivity, to derive fundamental limits to radiative heat transfer applicable in near- through far-field regimes. The limits depend on the choice of material susceptibilities and bounding surfaces enclosing arbitrarily shaped objects. In this article, we apply these bounds to two different geometric configurations of interest, namely dipolar particles or extended structures of infinite area in the near field of one another, and compare these predictions to prior limits. We find that while near-field radiative heat transfer between dipolar particles can saturate purely geometric "Landauer" limits, bounds on extended structures cannot, instead growing much more slowly with respect to a material response figure of merit, an "inverse resistivity" for metals, due to the deleterious effects of multiple scattering; nanostructuring is unable to overcome these limits, which can be practically reached by planar media at the surface polariton condition.