Unconventional Thermal Rectification in Assemblies of Supertetrahedral T₃-Type Sn₄In₆Se₂₀ Clusters

Going beyond the conventional design paradigm with atoms as building blocks, we propose the concept of cluster-assembled thermal rectifiers comprising metal chalcogenide supertetrahedral clusters. Different from the experimentally reported T_4,∞ and T_5,∞, for the first time we assemble T₃-Sn₄In₆Se₂₀ clusters into a stable T_3,∞ framework without needing extra ions, based on which the thermal rectification (TR) effect is explored using machine-learning molecular dynamics and the mode-resolved phonon Boltzmann transport equation. The tetrahedron-shaped cluster assembly serves as a novel TR switch, where the open state shows an outstanding TR efficiency (∼40%) arising from the asymmetric lateral confinement due to not only the phonon particle behavior but also the phonon wave nature. The prism-shaped assembly has a symmetric skeleton but with asymmetric surface roughness induced by clusters, thus exhibiting an unusual TR effect, distinguished from atom-based symmetric systems with atomically flat surfaces. Our findings demonstrate the unique potential of cluster assemblies for unconventional thermal rectification.