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Selectable diffusion direction with topologically protected edge modes

Topological insulators provide great potentials to control diffusion phenomena as well as waves. Here, we show that the direction of thermal diffusion can be selected by the contributions of the topologically protected edge modes via the quantum spin Hall effect in a honeycomb-shaped structure. We demonstrate that when we set our structure to the temperature corresponding to the type of edge mode, the direction of thermal diffusion can be tuned. Moreover, this diffusion system is found to be immune to defects owing to the robustness of topological states. Our work points to exciting new avenues for controlling diffusion phenomena.