Anharmonic Effects in Solids

This lecture delves into anharmonic effects in solids, exploring the implications of third-order terms in the potential energy, the breakdown of harmonic approximations, and the introduction of asymmetry. It further discusses thermal expansion, thermal conductivity, and the scattering of phonons. The instructor covers the impact of anharmonic terms on thermal resistance, the conservation of energy and momentum, and the scattering processes involving phonons. Additionally, the lecture touches on the quantum picture of heat capacity, the Debye model, and the failures of harmonic approximations in explaining thermal expansion. The session concludes with insights into the normal and Umklapp processes of phonon scattering and the vanishing resistance in superconductors.