Exploring the limits of super-Planckian far-field radiative heat transfer using 2D materials

TL;DR

This paper theoretically demonstrates that two-dimensional materials can exhibit far-field radiative heat transfer exceeding Planck's law by over seven orders of magnitude, with tunable effects in materials like graphene and black phosphorus.

Contribution

It reveals the potential for super-Planckian far-field heat transfer in 2D materials, surpassing previous limits and providing insights into their radiation mechanisms.

Findings

Heat transfer can exceed Planck's limit by over 7 orders of magnitude.

Tunable radiative heat transfer in graphene via external gating.

Surface plasmons are not involved in the dominant guiding modes.

Abstract

Very recently it has been predicted that the far-field radiative heat transfer between two macroscopic systems can largely overcome the limit set by Planck's law if one of their dimensions becomes much smaller than the thermal wavelength ($\lambda_{\rm Th} \approx 10\, \mu$m at room temperature). To explore the ultimate limit of the far-field violation of Planck's law, here we present a theoretical study of the radiative heat transfer between two-dimensional (2D) materials. We show that the far-field thermal radiation exchanged by two coplanar systems with a one-atom-thick geometrical cross section can be more than 7 orders of magnitude larger than the theoretical limit set by Planck's law for blackbodies and can be comparable to the heat transfer of two parallel sheets at the same distance. In particular, we illustrate this phenomenon with different materials such as graphene, where the radiation can also be tuned by a external gate, and single-layer black phosphorus. In both cases the far-field radiative heat transfer is dominated by TE-polarized guiding modes and surface plasmons play no role. Our predictions provide a new insight into the thermal radiation exchange mechanisms between 2D materials.