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Re: Thanks....

Of course I meant 'Fermi velocity' . To take a typo and make it into a question is 'sophomoric', Jneutron.
I don't think that I ever saw the response from the 'grad student' of Dr. Hummel's. Why don't you post it sometime?
I contacted Dr. Hummel, himself, about the difference between drift velocity and Fermi velocity, and how it changed the situation. He told me that the classical expression using drift velocity to predict current flow was a pretty good approximation for many situations, BUT that it failed with many elements such as sodium, etc. That is why the quantum expression of the same phenomena is so necessary. The quantum expression does not exclude a 'virtual' drift velocity, but it does change the number of donor electrons to some other value that is different from the classical expression. If the number of displaced electrons per unit volume is actually different in the quantum mechanical case, then it seems to me that the actual drift velocity would be different than the classically derived drift velocity, because you have a different number of electrons per unit volume to work with. How much different is still a question that I have, because it has NOT been stated by anyone, including Dr. Hummel.
However Dr. Hummel did state in (7.16) on p.82 that: j=v(F)eN' rather than j=Nve, where v in this case is the classical drift current, and v(F) is the Fermi velocity. This also inplies that N' should be a much smaller value than N, because the Fermi velocity is so fast, relative to the classical drift velocity. What do you think?

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