Dynamics of Long-Wavelength Phonons Near Boundaries and Interfaces in Nanomaterials

Long-wavelength phonons undergo infrequent phonon-phonon scattering and thus tend to propagate ballistically over long distances in single-crystalline, high-quality bulk materials, thereby making a major contribution to thermal conductivity in these systems. The dynamics of long-wavelength phonons and their interaction with boundaries and interfaces can be accurately modeled within the elastic-continuum limit. I will present recent work, combining experiment and theory, that shows phenomena such as the incoherent-to-coherent transition in thermal transport in III-V superlattices and the changes in the power-law dependence of phonon lifetime on frequency for rough nanowires and membranes with varying correlation types. The work illustrates the complexity of phonon interaction with disorder, and the utility and flexibility of numerical techniques such as the finite-difference time-domain (FDTD) method for elucidating the dynamics of phonons in nanomaterials.