Ultralow lattice thermal conductivity and glass-like thermal transport induced by double stacking faults in monolayer MS2 (M = Mo, W)

Ultralow lattice thermal conductivity (κL) is critical for enhancing thermoelectric efficiency and thermal barrier performance. Utilizing density functional theory and the unified theory, we systematically investigate the lattice dynamics and thermal transport properties in monolayer MS2 (M = Mo, W), containing two adjacent stacking faults (two-SFs). Compared to their intrinsic monolayers, we find that the two-SFs MoS2 possess a substantial suppression of κL. Microscopically, the order of reduction of κL mainly arises from the reduction of phonon group velocity and the significant enhancement of the three-phonon scattering rates, which originate from the combination of increased three-phonon scattering channels and hardened third-order interatomic force constants. The enhancement of three-phonon scattering channels is due to the closed acoustic–optical (a–o) gap in two-SFs MoS2. As temperature increases, two-SFs MoS2 exhibit hierarchical phonon thermal transport. Diffusons dominate thermal transport and break the conventional κL∝T−1 dependence, making κL display glass-like behavior. These insights may provide some perspectives for the potential applications of transition metal dichalcogenides in thermoelectric and micro/nanoelectronic devices, carry broad implications for phonon physics and thermal engineering in two-dimensional material systems, and reveal the regime of multimodal phonon transport generated by introducing periodic stacking faults.