Week 2

Lecture 17, 8 April, 10.00-12.00, FL51

Dynamics of lattice.

Reading.

A&M: Chapter 22.

Review questions.

1. What is the harmonic approximation and when is it valid? What is meant by the adiabatic approximation?
2. Explain the concepts of normal modes and dispersion curves. What are acoustic and optical branches? Explain their origin and their characteristic dispersion curves.
3. What is the dynamical matrix?
4. How many phonon states are in the 1BZ? How is the number of phonon branches related to dimensionality and the basis of a crystal?

Lecture 18, 11 April, 13.15-15.00, FL51

Dynamics of lattice.

Reading.

A&M: Chapter 22.

Review questions.

1. Derive the normal modes and the dispersion curve for a mono-atomic 1D Bravais lattice with nearest neighbour interactions in the harmonic approximation. Same for the lattice with basis.

Home task.

A&M: problem 22.3.