Difference between an optical and an acoustic phonon

Click For Summary
SUMMARY

The discussion clarifies the distinction between optical and acoustic phonons, emphasizing that these two types arise in diatomic crystals based on their wave propagation characteristics. Acoustic phonons correspond to low wave numbers and propagate in phase, while optical phonons are associated with higher wave numbers and can move out of phase. The analogy of rotating a glass filled with water and sand effectively illustrates this concept. For deeper understanding, Leon Brillouin's book, "Wave Propagation in Periodic Structures," is recommended as a valuable resource.

PREREQUISITES
  • Understanding of phonon theory
  • Familiarity with diatomic crystal structures
  • Knowledge of wave propagation concepts
  • Basic principles of solid-state physics
NEXT STEPS
  • Read the Wikipedia article on phonons for foundational knowledge
  • Study Leon Brillouin's "Wave Propagation in Periodic Structures" for advanced insights
  • Explore the mathematical modeling of phonon dispersion relations
  • Investigate experimental techniques for observing phonon behavior in materials
USEFUL FOR

Students and researchers in solid-state physics, materials scientists, and anyone interested in the fundamental properties of phonons in crystalline structures.

learner@123
Messages
10
Reaction score
0
Hello friends.
My question consists two parts,
1-What is the difference between an optical and an acoustic phonon?
1-What are the conditions by which we can decide the type of phonon i.e optical or acoustic phonon ?
Hope to get the reply soon.
 
Physics news on Phys.org
The two branches arise in diatomic crystals where phonons can propagate in a band or branch that has small (sound or acoustic) or large (infrared, typically, hence optical) wave numbers. Have you read the wiki article on phonons? That's a good place to start. Leon Brillouin's book Wave Propagation in Periodic Structures (or something like that) has an exceptionally clear and intuitive treatment, if you want to dig further.
 
Fill a glass with water and sand. Rotate the glass about it's axis in a sinusoidal fashion. If you rotate slowly enough, the particles will move roughly in phase with the glass. If you rotate fast enough, the particles will begin to move out of phase with the glass. This is analogous to acoustic and optical phonons.
 
  • Like
Likes   Reactions: jubaer145

Similar threads

  • · Replies 2 ·
Replies
2
Views
4K
  • · Replies 9 ·
Replies
9
Views
11K
  • · Replies 1 ·
Replies
1
Views
5K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 4 ·
Replies
4
Views
9K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 4 ·
Replies
4
Views
2K
Replies
5
Views
3K
  • · Replies 11 ·
Replies
11
Views
4K
  • · Replies 1 ·
Replies
1
Views
1K