Complex role of strain engineering of lattice thermal conductivity in hydrogenated graphene-like borophene induced by high-order phonon anharmonicity

Strain engineering has been used as a versatile tool for regulating the thermal transport in various materials as a result of the phonon frequency shift. On the other hand, the phononic bandgap can be simultaneously tuned by the strain, which can play a critical role in wide phononic bandgap materials due to the high-order phonon anharmonicity. In this work, we investigate the complex role of uniaxial tensile strain on the lattice thermal conductivity of hydrogenated graphene-like borophene, by using molecular dynamics simulations with a machine learning potential. Our findings highlight a novel and intriguing phenomenon that the thermal conductivity in the armchair direction is non-monotonically dependent on the uniaxial armchair strain. Specifically, we uncover that the increase of phonon group velocity and the decrease of three-phonon scattering compete with the enhancement of four-phonon scattering under armchair strain, leading to the non-monotonic dependence. The enhanced four-phonon scattering originates from the unique bridged B-H bond that can sensitively control the phononic bandgap under armchair strain. This anomalous non-monotonic strain-dependence highlights the complex interplay between different mechanisms governing thermal transport in 2D materials with large phononic bandgaps. Our study offers valuable insights for designing innovative thermal management strategies based on strain.