In solid state physics, I learned that the velocity of a bloch electron is ##\frac{\partial E(k)}{\partial k}##, where ##E(k)## is the energy dispersion. This formula is derived on the basis of the assumption that electrons is a wave packet of bloch state in solids.(adsbygoogle = window.adsbygoogle || []).push({});

However, I have a question concerning this statement:

I learned solid state physics three years ago and I am now a Ph.D. student. However, I still cannot convince me of the original statement because I know a wave packet BREAKS DOWN with time evolution. I can't imagine this formula can describe long time evolution of electron states.

Can anyone give me some confidence of this formula?

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# Wave packet description of electrons in solid state physics

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