Enhanced in-plane thermal conductivity of polar SrTiO3 by surface phonon polaritons within dual Reststrahlen band

Abstract

As device miniaturization advances, efficient nanoscale heat dissipation becomes increasingly critical. Surface phonon polaritons (SPhPs) offer fast, long-range channels for thermal transport. Dual Reststrahlen band materials such as SrTiO3 provide a broader SPhPs-supporting frequency range (Δω) and greater potential for enhancing SPhPs-mediated thermal conductivity (κ), yet their underlying mechanisms remain elusive. Herein, we analytically solve the SPhPs dispersion relations to investigate the influence of dual Reststrahlen bands on κ of SrTiO3, considering the effects of dielectric asymmetry (Δε) between the top and bottom surfaces of the membrane, temperature, and doping. We find that the low-frequency Reststrahlen band contributes more than two orders of magnitude higher κ than that outside the bands. Moreover, elevated temperatures and heavy doping reduce κ due to increased optical losses and diminished lattice polarization, particularly within the low-frequency Reststrahlen band. These findings complement the current understanding of SPhPs-mediated heat transport and suggest an alternative strategy for thermal management in nanoscale systems.