# Near-field heat transfer between graphene/hBN multilayers

## TL;DR

This study investigates how multilayer graphene/hBN structures influence near-field heat transfer, revealing hybrid polaritons' dominant role and the ability to modulate heat transfer via electrical gating and layer number.

## Contribution

It provides a detailed analysis of hybrid polaritons in multilayer graphene/hBN structures and highlights the limitations of effective medium theory in predicting heat transfer.

## Key findings

- Hybrid surface polaritons dominate heat transfer in multilayer structures.
- Effective hyperbolic behavior enhances photon tunneling and heat transfer.
- Heat transfer can be modulated by the number of graphene layers and electrical gating.

## Abstract

We study the radiative heat transfer between multilayer structures made by a periodic repetition of a graphene sheet and a hexagonal boron nitride (hBN) slab. Surface plasmons in a monolayer graphene can couple with a hyperbolic phonon polaritons in a single hBN film to form hybrid polaritons that can assist photon tunneling. For periodic multilayer graphene/hBN structures, the stacked metallic/dielectric array can give rise to a further effective hyperbolic behavior, in addition to the intrinsic natural hyperbolic behavior of hBN. The effective hyperbolicity can enable more hyperbolic polaritons that enhance the photon tunneling and hence the near-field heat transfer. However, the hybrid polaritons on the surface, i.e. surface plasmon-phonon polaritons, dominate the near-field heat transfer between multilayer structures when the topmost layer is graphene. The effective hyperbolic regions can be well predicted by the effective medium theory (EMT), thought EMT fails to capture the hybrid surface polaritons and results in a heat transfer rate much lower compared to the exact calculation. The chemical potential of the graphene sheets can be tuned through electrical gating and results in an additional modulation of the heat transfer. We found that the near-field heat transfer between multilayer structure does not increase monotonously with the number of layer in the stack, which provides a way to control the heat transfer rate by the number of graphene layers in the multilayer structure. The results may benefit the applications of near-field energy harvesting and radiative cooling based on hybrid polaritons in two-dimensional materials.