Cooperative Suppression Strategy for Dual Thermal Transport Channels in Crystalline Materials

Abstract

We propose a novel design principle for achieving ultralow thermal conductivity in crystalline materials via a "heavy-light and soft-stiff" structural motif. By combining heavy and light atomic species with soft and stiff bonding networks, both particle-like (${\kappa }_p$) and wave-like (${\kappa }_c$) phonon transport channels are concurrently suppressed. First-principles calculations show that this architecture induces a hierarchical phonon spectrum: soft-bonded heavy atoms generate dense low-frequency modes that enhance scattering and reduce ${\kappa }_p$, while stiff-bonded light atoms produce sparse high-frequency optical branches that disrupt coherence and lower ${\kappa }_c$. High-throughput screening identifies Tl${}_4$SiS${}_4$ (${\kappa }_p$ = 0.10, ${\kappa }_c$ = 0.06 W/mK) and Tl${}_4$GeS${}_4$ (${\kappa }_p$ = 0.09, ${\kappa }_c$ = 0.06 W/mK) as representative candidates with strongly suppressed transport in both channels. A minimal 1D triatomic chain model further demonstrates the generality of this mechanism, offering a new paradigm for phonon engineering beyond the conventional ${\kappa }_p$-${\kappa }_c$ trade-off.