Phonon coherent transport leads to an anomalous boundary effect on the thermal conductivity of a rough graphene nanoribbon
Shuang Tian, T.S. Wang, Hao Chen, Dengke Ma, Lifa Zhang
Abstract
Coherent phonons can give rise to phenomena and physical mechanisms in different systems. Understanding phonon-boundary scattering is critical for the manipulation of thermal properties. In this paper, it is found that the thermal conductivity of rough graphene nanoribbon first monotonically changes, and then exhibits an oscillatory manner with the varying of surface boundary roughness. An obvious increase in thermal conductivity, up to 25.33%, can be observed as surface boundary roughness increases from 0.61 to 0.72. This is in contrast to the conventional understanding that thermal conductivity typically decreases when surface boundary roughness increases. Further, a frequency-resolved picture and lattice dynamics analysis identify that the anomalous boundary effect originates from the coherent nature of phonons, which results in the roughness-selected destructive interference of different modes. Besides, the oscillation will be reduced by introducing rough boundaries with different sinusoidal shapes, which increases the randomness. This abnormal boundary effect can also be extended to other materials, for example, hexagonal boron nitride monolayer, depending mainly on the anharmonicity. The study reveals physical insights into phonon-boundary scattering and may aid the design of heat management and thermoelectric devices based on the boundary effect.