Interacting Systems and Quasiparticles
The “classical” picture we have of a solid consists of the ion cores fixed in a matrix around which the interacting electrons are essentially free to move throughout the whole crystal. In quantum terms we would like to replace this, as far as possible, by a set of single-particle states (in the sense of the Hartree or Hartree-Fock approximation), so that we could calculate the various properties of the solid. The true eigenstates of the system are too difficult to work with, however, and, even if we knew them, they would certainly not be single-particle states. The desire to use a single-particle approach, coupled with the real success of the single-particle calculations of the properties of solids, requires us, as far as possible, to think in terms that approximate the ideal single-particle system. Suppose we derived a set of single-particle states, then a useful criterion as to how good they were would be how long the electron was able to remain in that state.
KeywordsWave Packet Fermi Surface Quasi Particle Phonon Emission Finite Lifetime
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