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

Abstract

Thermal rectification is a two-terminal property: the same device must carry different heat-current magnitudes when two reservoir temperatures are interchanged. In this Comment on Ref.~\cite{WuHu2026}, we ask whether the reported ratio $γ=R_{\mathrm{f}}/R_{\mathrm{b}}$ can represent such a two-terminal rectification ratio within the fixed-background linearized phonon Boltzmann transport equation (BTE) used in that work. We show that, for a passive two-terminal reservoir problem, any fixed linearized BTE whose scattering operator preserves a uniform equilibrium temperature shift, and whose boundary-value problem is well posed, gives equal forward and reverse resistance magnitudes. A direction-dependent response can still occur under a prescribed gradient-weighted source--sink protocol, but such a response should be distinguished from two-terminal thermal rectification.