Fundamental limit of phonon Tesla valve for heat rectification from first principles

Directional control of heat remains a central challenge for energy conversion, waste-heat utilization, and thermal management, as existing thermal rectifiers exhibit low efficiency or operate only at cryogenic temperatures. Here we demonstrate giant phonon rectification in solid-state "phonon Tesla valves", inspired by Nikola Tesla's fluidic one-way valve but governed by fundamentally different transport physics. Using ab initio Boltzmann transport simulations with full scattering matrices, we show that hydrodynamic phonon transport in graphite coupled with asymmetric valve geometry produces strong forward-backward contrast in phonon relaxation. Single-stage devices achieve rectification ratios of up to approximately 8, while multistage configurations reach ratios of approximately 16, far exceeding those of prior thermal diodes. The rectification mechanism originates from asymmetric relaxation of nonequilibrium phonons at diffusive boundaries, in contrast to inertia-driven fluid Tesla valves. These results examine the performance limits of phonon Tesla valves and establish a platform for directional heat control and highlight the unique potential of hydrodynamic phonons for thermal information processing and energy technologies.