One-Electron Excitations vs. Collective Excitations in the 1D Falicov-Kimball Model with Hund Coupling at Half Filling

Abstract

The Falicov-Kimball model enriched with Ising-type Hund coupling between spins of itinerant electrons and magnetic ions is studied exactly on finite 1D rings. At half filling (one electron per site) and for the density of magnetic ions equal to 1/2 it is shown that many-electron collective excitations coupled to spin reorientations of the magnetic ions have much lower energy than single electron excitations. This property is caused by energy gaps formed at the Fermi levels in one-electron energy spectra of all relevant magnetic configurations of the ions. Consequently, low temperature properties of the system are not driven by one-particle, elementary electron excitations but many-particle collective excitations, where both electrons and spins of magnetic ions are involved. In addition, it is shown that many-body excitation spectra derived both from spin fluctuations and from charge fluctuations have a regular structure.

Energy spectrum analysis and finite temperature properties of the Falicov-Kimball model with Hund coupling at half filling

“…12 In the PM the magnetic excitations spectrum is composed of separated parts characterized by fixed numbers of the NN pairs of magnetic ions coupled ferromagnetically. The higher part of the magnetic excitation spectrum has more increasingly NN ferromagnetic pairs occurring.…”

“…͓It is noteworthy that a similar regular structure of the energy spectrum was also found in the one-dimensional ͑1D͒ system. 12 …”