Coherence lengths in electron-phonon scattering

Abstract

It is shown that the normally accepted condition for the independence of electron-phonon and electron-impurity scattering, q lambda >>1, is wrong and a much stronger condition is needed: q( lambda lambda _F/4 pi )¹2/>>1 in a free electron approximation, where lambda _F is the de Broglie Fermi wavelength. Experimental evidence is cited to support this contention, and it is pointed out that analogues exist in optics.