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Description
We investigate the nanoscale mechanisms determining in-plane lattice thermal conductivity (LTC) of pristine and W-doped MX$_2$-M$^{\prime}$X$^{\prime}_2$ transition metal dichalcogenide heterobilayers in both phonon and relaxon bases. For the W-doped systems, we evaluate the anharmonic force constants using machine-learning potentials trained on first-principles data. Pristine heterobilayers exhibit isotropic LTC with preserved ordering across temperature. Under nearest-neighbour chalcogen substitution the LTC follows the ordering Te < Se < S; relaxon analysis further links the LTC and viscosity to harmonic phonon descriptors including phonon mode layer localisation and cophonicity. A sufficiently large mass contrast is required to induce layer localisation of the transport-relevant phonon modes, leading to enhanced LTC. The viscosity, which correlates positively with LTC, is associated with the low-cost cophonicity descriptor. Doped heterobilayers exhibit reduced and anisotropic LTC across all temperatures, while the aforementioned descriptors no longer correlate with the LTC. We find that the direction of maximum LTC can in principle be modulated by composition and temperature, although future work is required to establish robustness of the LTC magnitude and anisotropy trends. Thanks to its general formulation the analysis protocol can be readily extended to other van der Waals heterostructures, and the descriptors may be implemented in high-throughput engines to identify promising layered materials with tailored thermal transport characteristics.
This work was co-funded by the European Union under the project “Robotics and advanced industrial production” (reg. no. CZ.02.01.01/00/22_008/0004590), by the Czech Science Foundation project No. 24-12643L, and by the Ministry of Education, Youth and Sports of the Czech Republic through the e-INFRA CZ (ID: 90254).