[kragen]

while of course that is correct, that's not what i'm talking about

there is a good introductory presentation in https://www.feynmanlectures.caltech.edu/III_13.html but note that it assumes some previous familiarity with quantum mechanics. §13.6 explains that mostly what the electrons (really propagating waves of quantum probability amplitude for there to be an extra electron) are scattering off of is imperfections in the lattice. but that can't be the whole story or all perfect crystals would be superconductors