PHYSICS · Multi-part · Fermi University Physics · Condensed Matter, Materials & Soft Matter · Lattice dynamics and thermal properties of solids · Lattice dynamics and thermal properties of solids
Condensed Matter Physics, Ch Two atoms in the cell: acoustic and optical branches
Problem
A diatomic chain has M2=3M1. At the zone boundary, a mode is found in which the heavier ion is fixed and the lighter ion oscillates.
((a)) Is this mode acoustic or optical?
((b)) Describe, in one sentence, what the same two ions do in the other branch at the same wavevector.