Question

1.
(a) Estimate the size of the phonon energy gap in NaCl relative to the energy of an acoustic phonon at the Brillouin zone, using the diatomic linear chain model.

(b) Using the dispersion relation for the diatomic linear chain model, demonstrate that the group velocity vanishes on approach to the Brillouin zone edge for both the acoustic and optical branches.

Please show each step with explanation, if possible. Thank you in advance.

Answer 1

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