Dynamical Mean-Field Theory of Spin Fluctuations

Abstract

In the mean-field or HF theory of itinerant electron magnetism, a thermal spin-flip excitation of an electron across the Fermi level is considered and an electron and a hole thus produced are assumed to move independently in a common static mean field. The resulting spin density fluctuation has generally a small amplitude and the thermal excitation is underestimated. To be more realistic we have to take into account the scattering of electron-hole pairs due to the exchange interaction. This gives rise to the exchange-enhanced spin density fluctuations including spin waves as bound collective modes of electron-hole pairs.