A few questions for self-controlling

Elastic properties

• What are stress and strain and how are they linked?
• What are suppositions applied in elasticity theory?
• What is shear stress?
• How to measure sound velocities? Why there is more than one of them?
• What to learn from these experiments on microscopic propeties of a material?

Phonons:

• What is an acoustic branch?
• Is there always an optical branch? Why?
• Why restricting to the 1st BZ is sufficient?
• Btw, what is the BZ?
• How fast do acoustic wave propagate at q=0, q=pi/a?
• How many branches do you expect for a system with 5 atoms per unit cell?
• Are in general longitudinal or transversal sound waves faster?
• Sketch a typical phonon branch and discuss it

• What is a phonon?
• Write energy and momentum conservation laws for an inelastic neutron scattering experiment
• Why a phon is considered a quasi-particle?
• How to experimentally determine the phonon dispersion of a material?
• How many phonons can be excited in a material? Discuss...
• Can one excite phonons with optical light?
• Explain Raman scattering
• Explain Brillouin scattering

• What is the density of states?
• ... and why is it considered so relevant?
• How to calculate the DOS of a given material?
• Does DOS depend on the dimension of a system?
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