11. It begins with transitions at the center of the Brillouin zone , \ boldsymbol { k } = 0. 12. Brillouin was a founder of modern solid state physics for which he discovered, among other things, Brillouin zones . 13. Physically, U-processes occur when the final momentum of the particle points out of the first Brillouin zone . 14. Photons have negligible wave vectors and therefore the band extremes have to be in the same position of the Brillouin zone . 15. An ACAR measurement on a metal has discontinuities where bands cross the Fermi level in all Brillouin zones in reciprocal space. 16. Optical phonons have a non-zero frequency at the Brillouin zone center and show no dispersion near that long wavelength limit. 17. The most important consequence of the periodic potential is the formation of a small band gap at the boundary of the Brillouin zone . 18. During his work on the propagation of electron waves in a crystal lattice, he introduced the concept of Brillouin zones in 1930. 19. A constant force F _ 0 results in the acceleration of the particle until the edge of the first Brillouin zone is reached. 20. Therefore, all distinct Bloch waves occur for "'k "'- values within the first Brillouin zone of the reciprocal lattice.
