Phonon Transport in the Gigahertz to Terahertz Range: Confinement, Topology and Second Sound

This work offers perspectives on phonon-transport studies in the gigahertz (GHz) to terahertz (THz) range [Journal of Applied Physics 131, 180901 (2022)]. The transport of heat and sound in the GHz-THz range is important for thermal management in electronic devices, signal-processing with microwave radiation, and various types of sensing applications with nanomechanical resonators. In this article we descibe frequency-domain techniques for remote, non-destructive, and all-optical detection of GHz-THz phonons using Brillouin light scattering and frequency-domain thermoreflectance