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 M1<M2. For each of the four amplitude relations below, say whether it belongs to the acoustic or the optical branch, whether it holds at the zone centre (q=0) or the zone boundary (q=π/a), and describe in one sentence how the two ions move.
((a)) U=W
((b)) M1U+M2W=0
((c)) the light ion is at rest, the heavy ion oscillates alone
((d)) the heavy ion is at rest, the light ion oscillates alone