9:30 AM - 11:30 AM
▲ [20a-PB4-8] Phonon Annihilation and Creation Processes: A Wavelet Transform Approach
Keywords:Phonon annihilation and creation, Phonon coherence time
The understanding of thermal transport in nano-devices and low-dimensional materials remains a crucial topic nowadays, as related applications exist in several fields, such as thermal management and thermoelectrics, etc. Thermal conductivity is usually determined by the scatterings of heat carriers, such as the inherent phonon-phonon scattering, which are commonly described by the Boltzmann transport theory. However, the ‘real’ dynamic process of phonons, i.e. when and where the phonon are created and annihilated, is still mysterious. On the other hand, phonons are naturally vibration waves. Recently, experimental works demonstrated that in phononic crystals, wave-like phonons, i.e. coherent phonons, possess significant contributions to thermal transport. However, the existing picture of phonon transport is essentially based on the particle vision. The exploration of the real physical phonon behaviour becomes a critical challenge in the phononic community.In this work, we propose a wavelet transform approach that is based on a decomposition into wave packets of the atomic motions, to study the time-dependent phonon dynamics. Based on the modelling of atomic motions in graphene from molecular dynamic simulations, the wavelet transform clearly reveals the phonon creation and annihilation process via phonon fluctuations. We also found that phonon creation and annihilation processes have different characteristic times, and shows wavevector dependence. Moreover, the diversity of mode coherence times of phonons are demonstrated, and the coherence time is close to the lifetime of wave packets. Our work provides a real and direct image of phonon dynamics expressing phonon-phonon scatterings in thermal transport. Moreover, the wavelet transform also establishes a real picture of phonons including both wave and particle nature of phonons.