Hydrodynamically enhanced thermal transport due to strong interlayer interactions: A case study of strained bilayer graphene

Manipulating interlayer interactions in two-dimensional (2D) materials is a widely used and effective method for regulating heat transport, which is important for thermal management of electronics. In this paper, we find that thermal transport can be enhanced by strong interlayer interactions. For instance, 2D bilayer materials with interlayer bonding have larger thermal conductivity than their monolayer counterparts. To further verify the conjecture, we take bilayer graphene (BLG) as a study case to gradually strengthen the interlayer interactions in BLG by applying a series of compressive strains along the out-of-plane direction. It is found that the thermal conductivity of BLG first decreases and then anomalously increases when the strain is larger than the threshold of 12%. For the decreasing trend, it is mainly due to the strain-induced reduction of phonon group velocity and lifetime. While at larger strain (>12%), the anomalous increase of thermal conductivity is found to be caused by hydrodynamic phonon transport and weak phonon anharmonicity. Thus, enhanced interlayer interactions can enhance the hydrodynamic phonon transport and thus improve the heat transfer performance. In this paper, we not only report the hydrodynamic enhancement of thermal transport through enhanced interlayer interactions but also provide solid evidence. These findings will deepen the understanding of thermal transport in layered materials and heterostructures, which will benefit the applications in thermal management.