Quasi-Ballistic Heat Conduction of Long-Range Surface Phonon Polaritons Coupled to Thermal Reservoirs

Rigorous thermal control at the nanoscale has become essential with the miniaturization of electronic devices. However, heat transfer in such structures is hindered by increased boundary scatterings and reduced thermal conductivity. Surface phonon polaritons (SPhPs), arising from the coupling of optical phonons and photons in the mid-IR regime, present a promising solution as long-range heat carriers capable of circumventing the limitations faced by traditional heat carriers such as acoustic phonons in nanoscales. However, the detection and utilization of SPhP-mediated thermal conduction have proven to be challenging. Here, we introduce an innovative approach that employs a grating-integrated thermometry platform, specifically designed to enhance the transmission of SPhP modes with long decay lengths and detectability of SPhPs over short, ballistic distances. We demonstrate quasi-ballistic, length-independent thermal conduction mediated by long-range SPhPs in one-dimensional SiO₂ heat channels, achieving a SPhP thermal conductivity of 1.5 W/m K, which has been over 90% of the intrinsic thermal conductivity.