Phonon-Localization-Driven Decoupling of Dual-Channel Transport for Record-Low Intrinsic Lattice Thermal Conductivity

Abstract

A fundamental bottleneck in pushing the intrinsic lattice thermal conductivity of inorganic crystalline solids to its lowest limit arises from the inherent competition between the particle-like propagation (\(κ_{\mathrm{L}}^{\mathrm{P}}\)) and wave-like tunneling (\(κ_{\mathrm{L}}^{\mathrm{C}}\)) channels. Herein, we demonstrate that phonon localization provides a robust pathway to decouple the dual-channel transport, achieving record-low \(κ_{\mathrm{L}}\) in quasi-1D ternary helical crystals. Despite the structural complexity leading to densely populated phonon branches and thus inducing abundant coherent phonons, the weak interchain interactions and heavy elements compress numerous branches into highly localized, nearly dispersionless flat bands. Such strong localization simultaneously suppresses both the diagonal and off-diagonal components of the group velocity, thereby synergistically suppressing \(κ_{\mathrm{L}}^{\mathrm{P}}\) and \(κ_{\mathrm{L}}^{\mathrm{C}}\). Taking InSeI as an example, the interchain room-temperature \(κ_{\mathrm{L}}^{\mathrm{P}}\) and \(κ_{\mathrm{L}}^{\mathrm{C}}\) are 0.145 and 0.053 W/mK, respectively, yielding an ultralow total \(κ_{\mathrm{L}}\) of 0.198 W/mK. Weaker interchain interactions further drive the room-temperature \(κ_{\mathrm{L}}\) of GaSeI and AlSeI to record lows of 0.086 and 0.089 W/mK, respectively; these values even drop to 0.058 and 0.059 W/mK at 900 K. These findings provide useful insights into exploring the thermal conductivity limit in crystals.