13  Electron–Phonon Coupling (optional)

NoteLearning Objectives

By the end of this lecture, you should be able to:

• explain why lattice vibrations modulate the electronic potential and therefore scatter Bloch electrons;
• derive the linearized form of the electron–phonon perturbation from small ionic displacements;
• state the crystal-momentum and energy selection rules for phonon absorption and emission;
• explain the deformation-potential picture for long-wavelength longitudinal acoustic phonons;
• connect electron–phonon scattering to electrical resistivity, electronic thermal conductivity, and finite phonon lifetimes;
• interpret phonon broadening and softening as observable consequences of electron–phonon coupling.