Optical phonons on thermal conduction in advanced materials

The requirements for high performance, reliability, and longevity in electronic devices, such as power semiconductors and thermal sensors, make effective thermal management a formidable challenge. Thus, understanding lattice dynamics is crucial for regulating thermal conduction, as the intrinsic limit mainly depends on phonon dispersions. Conventionally, thermal conduction is regulated through heat-carrying acoustic phonon manipulation due to their high group velocities, which are widely utilized in materials such as thermal coatings and thermoelectrics. In recent years, with advancements in thermal transport, optical phonons have been of great interest for tuning thermal conduction, with a particular focus on those with special dispersive behaviors; however, the microscopic mechanisms are significantly different. This review aims to provide a comprehensive understanding of the effect of optical phonons, especially those with high weights on thermal conduction in advanced materials, as well as discuss the fundamental mechanisms, including (i) phonon bandwidth, (ii) phonon gap, (iii) avoided-crossing, (iv) phonon nesting/twinning, (v) optical-acoustic phonon bunching, and (vi) multiple optical phonons.