Abstract

Phonons and related processes govern the thermal properties of materials. They can be excited externally using light, heat, mechanical energy, etc. This article aims to elucidate the methodology used in studying thermal properties, specifically employing temperature-dependent Raman spectroscopy. However, unique challenges arise when applying these techniques to low-dimensional materials. We summarize theoretical and experimental studies highlighting the significance of phonon hydrodynamics—a phenomenon typically observed only at low temperatures in bulk materials, but now found at room temperature in 2D materials like graphene. This discovery calls for caution when utilizing temperature-dependent Raman spectroscopy-based techniques, such as the optothermal Raman method, which has been extensively employed to experimentally determine the thermal conductivity of graphene. Moreover, temperature-dependent Raman spectroscopy remains a valuable tool for investigating phonon anharmonicity, a key factor governing phonon transport and decay processes in a wide array of emerging 2D materials and their heterostructures.