Optimally Suppressed\nPhonon Tunneling in van der Waals\nGraphene–WS<sub>2</sub> Heterostructure with Ultralow Thermal\nConductivity

Van der Waals heterostructures have great potential for\nrealizing\nultimately low thermal conductivity because defectless interfaces\ncan be constructed at a length scale smaller than the phonon wavelength,\nallowing modulation of coherent phonon transport. In this Letter,\nwe demonstrate the mechanism for thermal conductivity reduction at\na mode-resolved level. The graphene–WS<sub>2</sub> heterostructure\nwith the lowest cross-plane thermal conductivity of 0.048 W/(m·K)\nis identified from 16,384 candidates by combining Bayesian optimization\nand molecular dynamics simulations. Then, the angle-resolved phonon\ntransmission is calculated using the mode-resolved atomistic Green’s\nfunction. The results reveal that the optimal heterostructure nearly\ncompletely terminates phonon transport with finite incident angles,\nowing to the reduced critical incident angle and suppression of phonon\ntunneling.