Polaritonic Waveguide Emits Super-Planckian Thermal Radiation

TL;DR

This paper demonstrates experimentally that coating non-absorbent bodies with an absorbent material to form a polaritonic waveguide can surpass Planck's limit of far-field thermal radiation, with potential applications in microelectronics.

Contribution

It introduces a novel method of exceeding Planck's thermal radiation limit using polaritonic waveguides formed by coating bodies, supported by experimental validation.

Findings

Radiative conductance exceeds Planck's limit by a factor of two.

Measured conductance aligns with SPhP waveguide mode predictions.

Super-Planckian radiation observed in coated silicon plates.

Abstract

Classical Planck's theory of thermal radiation predicts an upper limit of the heat transfer between two bodies separated by a distance longer than the dominant radiation wavelength (far-field regime). This limit can be overcome when the dimensions of the absorbent bodies are smaller than the dominant wavelength due to hybrid electromagnetic waves, known as surface phonon-polaritons (SPhPs). Here, we experimentally demonstrate that the far-field radiative heat transfer between two non-absorbent bodies can also overcome Planck's limit, by coating them with an absorbent material to form a polaritonic waveguide. This super-Planckian far-field thermal radiation is confirmed by measuring the radiative thermal conductance between two silicon plates coated with silicon dioxide nanolayers. The observed conductance is twice higher than Planck's limit and agrees with the predictions of our model for the SPhP waveguide modes. Our findings could be applied to thermal management in microelectronics and silicon photonics.