All Questions
7 questions
31
votes
5
answers
19k
views
Is crystal momentum really momentum?
Almost every solid state physics textbook says crystal momentum is not really physical momentum. For example, phonons always carry crystal momentum but they do not cause a translation of the sample at ...
- 1,515
6
votes
1
answer
2k
views
Why phonons are Goldstone modes?
I read this in the lecture notes by David Tong:
"Gapless excitations often dominate the low-temperature behaviour of a system, where they are the only excitations that are not Boltzmann ...
- 83
15
votes
1
answer
1k
views
Why is crystalline graphite black yet shiny?
I am unable to find images of pure crystalline graphite with high confidence, but based on various sources I believe that it should actually be both black and shiny, in the sense that it reflects much ...
- 2,916
10
votes
3
answers
24k
views
Can someone explain LO-TO Splitting?
LO-TO splitting occurs in an ionic (i.e. polar) solid such as GaAs or NaCl. What happens is that the degeneracy of the transverse optical (TO) and longitudinal optical (LO) phonons at $k=0$ is broken ...
- 2,897
4
votes
1
answer
539
views
How the number of atoms in the basis affects the density of states?
When dealing with phonons and specific heat of solids, it seems the really important quantity to obtain is the density of states $N(\omega)$. When we have it, we can find the internal energy as
$$U(T)...
- 37.4k
2
votes
1
answer
760
views
Why do we need the quantization for lattice vibration?
I've been reading the Wikipedia article on phonon. So, my understanding is what they get is the discrete energy levels of vibration from quantization. But the discrete energy level is not only the ...
- 479
1
vote
1
answer
591
views
How to understand crystal momentum, its relation to translational symmetry, Noether theorem, and to symmetry breaking/Landau-Ginzburg theory?
This question continues from my another question How to understand critical points of the Brillouin zone, (in)direct bands of transition-metal dichalcogenides?, and is related to Is crystal momentum ...
- 207