Feynman Diagrams and Green’s Functions in Itinerant Electron Magnetism
In this chapter we explore some basic problems of itinerant electron magnetism by applying the method of Green’s functions and Feynman diagrams. First we rederive the magnetic susceptibility and the phonon spectrum by using Feynman diagrams. Then we study how magnetism is involved in the electron self-energy due to the electron-phonon interaction (EPI). Such an observation leads to a new insight on the role of magnetism in superconductivity. We discuss also the electron self-energy due to spin waves, and spin fluctuations Finally, we critically review various current viewpoints on the role of the EPI in magnetism of a metal.
KeywordsFermi Surface Spin Wave Ferromagnetic State Paramagnetic State Spin Fluctuation
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