Tunable Asymmetric Thermal Transport via Phonon Polaritons Enhancement in Nanophotonic Cavities

Dynamic control of nanoscale heat flow is a pivotal challenge for thermal management in advanced integrated circuits and high‐power compact devices. Conventional phonon‐based modulation strategies are fundamentally restricted by the intrinsic crystalline lattice, exhibiting limited performance in modulation amplitudes and directional transport. This necessitates the exploration of new physical paradigms. Phonon polaritons, hybrid quasiparticles arising from phonon‐photon coupling, bridge thermal and electromagnetic transport, thus opening transformative possibilities for photonics‐based thermal control. Here, we demonstrate ultrahigh heat flow enhancement and active directional control of heat conduction through phonon‐polariton coupling enabled by nanophotonic cavities. Asymmetric graphene nanoresonators patterned on suspended silicon dioxide nanobeams launch and confine surface plasmon–phonon polaritons (SPPPs) that transport heat along the structure. By tailoring cavity geometry, the effective thermal conductivity increases from 1.48 to 4.73 Wm −1 K −1 , corresponding to a resonant enhancement of up to 219%. This enhancement arises from Fabry–Pérot resonances and Purcell‐type amplification of SPPP modes, while structural asymmetry further induces asymmetric SPPP excitation, yielding a thermal rectification ratio of 143%. Our results uncover an optical mechanism for amplifying and directing heat flow, expanding the application of nanophotonics into the thermal domain and establishing a foundation for polariton‐based reconfigurable thermal circuitry and optically controlled nanoscale heat management.