Significant progress in manipulating heat diffusion has been achieved with the advent of non-Hermitian physics and topology. However, previous studies on diffusive systems have primarily concentrated on isolated cases, where fields decay exponentially over time. In practical scenarios, systems inevitably interact with external environments, making it essential to study their responses to external heat signals. This, in turn, relies on analyzing the scattering behavior of these signals. In our work, we experimentally realize thermal scattering in a diffusive anti-parity-time (APT) system. We define key parameters of the temperature field—amplitude, phase, and chirality—and reveal that the scattering symmetry of the APT diffusive system only arises when temperature signals with different chiralities interact. Such mechanism is induced by the channel's intrinsic time-reversal antisymmetry (anti-T symmetry), which gives rise to unique dispersion properties in diffusive systems, where positive and negative frequencies are inequivalent, corresponding to different chiralities. Our findings therefore highlight the pivotal role of scattering channels in dictating the symmetry and phase transitions of non-Hermitian systems, and our work provides an experimental platform to observe and control these strongly dissipative phenomena.

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• Diffusion
• Metamaterials
• Non-Hermitian systems