I understand that interband transitions should be vertical because photons does not have a lot of momentum... But why non vertical transitions are allowed in metals? The electron shifts to a higher energy in the same band, and should also change it's momentum. Where did the extra momentum come from? Is this also possible for electrons on the conduction band? Like for doped semiconductors?
The momentum and the horizontal transition is given by the interaction between electrons and phonons, the normal modes of vibration of the crystal. This phenomenon is usually complementary with a vertical one and allows to reach the conductive bands with just the minimum energy gap even if the gap is non direct
I think this lecture would be phenomenal, if you fix your microphone. I can hear a very noticable high pitched sound whenever you speak which also amplifys with the volume of your voice... this makes it literally unwatchable for me. You could try to cut off very high frequencys in the audio and reupload it.
![BLACK BAG - Official Trailer [HD] - Only in Theaters March 14](http://i.ytimg.com/vi/Du0Xp8WX_7I/mqdefault.jpg)
I really liked to have a teacher like you.
Great lectures always!
Ну вот это можно назвать лекцией) Спасибо! Было бы круто если бы семинары в виде моделирований в Матлабе, чтобы почувствовать все это дело.
Very good lecture :D
I understand that interband transitions should be vertical because photons does not have a lot of momentum... But why non vertical transitions are allowed in metals? The electron shifts to a higher energy in the same band, and should also change it's momentum. Where did the extra momentum come from? Is this also possible for electrons on the conduction band? Like for doped semiconductors?
The momentum and the horizontal transition is given by the interaction between electrons and phonons, the normal modes of vibration of the crystal. This phenomenon is usually complementary with a vertical one and allows to reach the conductive bands with just the minimum energy gap even if the gap is non direct
50:00
6:00
I think this lecture would be phenomenal, if you fix your microphone. I can hear a very noticable high pitched sound whenever you speak which also amplifys with the volume of your voice... this makes it literally unwatchable for me. You could try to cut off very high frequencys in the audio and reupload it.
If you can follow Sergei, you can build your own Band-Pass and eliminate Hiss and Pops
You should install equalizer, whether on your OS or your browser to eliminate that sound. A physicist should be able to tackle his problems himself.