Near-field radiative heat transfer between nanoparticles mediated by acoustic phonon polaritons

Abstract

Phonon polaritons (PhPs) in natural hyperbolic materials exhibit a high density of electromagnetic states, enabling the efficient enhancement and manipulation of near-field energy transport. In this study, we theoretically investigate the substrate-mediated polaritonic effect on near-field radiative heat transfer between two nanoparticles (NPs) in proximity to a slab of biaxial hyperbolic material α-MoO₃. Compared to conventional PhPs in a freestanding α-MoO₃ slab, acoustic phonon polaritons (APhPs) supported by an α-MoO₃/dielectric spacer/gold heterostructure can either enhance or suppress near-field thermal radiation. This is attributed to the gap-dependent electromagnetic field confinement and propagation length of the APhPs, which jointly influence the radiative energy transfer. Interestingly, even when NPs are located near the α-MoO₃/gold heterostructure, thermal radiation can be suppressed in comparison to the system without a reflective surface. Furthermore, our research demonstrates an improvement in the near-field coupling between propagating APhPs and the localized surface modes of NPs by rotating the α-MoO₃ crystal around the [001] crystalline direction. Notably, we show that an in-plane rotated α-MoO₃ slab offers a modulation contrast ratio in radiative heat transfer exceeding 7000 between “ON” and “OFF” states. Therefore, these findings provide valuable guidance for controlling non-contact energy exchange at the nanoscale.