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Umklapp process 
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#1
Oct3013, 03:52 PM

P: 1,005

This occur when two phonons interact and the sum of their momenta add to a new wavevector outside the new Brillioun zone. The resulting wavevector is then mapped back into the Brillioun zone by subtraction of a suitable reciprocal lattice vector.
I don't think I understand the physics in all of this. I understand the idea but what is physically going on in this process and where does the leftover momentum go? 


#2
Oct3013, 04:11 PM

Sci Advisor
Thanks
PF Gold
P: 1,908

The left over energy absorbed by the crystal; the momentum is not "real momentum"  it is crystal momentum, which is not conserved.
See http://www.physicsforums.com/showthread.php?t=715639 


#3
Oct3113, 01:59 AM

Sci Advisor
P: 3,593

Well, of course also real momentum is conserved. It is taken up completely by the lattice.



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