抄録
Four types of magnetic exchange interactions, which work between quasiparticles, are investigated within the theoretical frameworkof the virtual exchange of bosons or bosonic excitations.Three types of exchange interactions are due to the virtual exchange of high-energy spin excitations, pair excitations of electrons far from the chemical potential through the spin channels.They are characterized by a pair of intermediate states in the exchange process; the conventional superexchange interaction is characterized by a pair of occupied bands, an extended superexchange interaction by a pair of unoccupied bands, and an extended Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interaction by a pair of an occupied band and an unoccupied band.These three types of exchange interactions are present in both insulating and metallic states.The fourth one is a novel exchange interaction due tothe virtual exchange of low-energy spin excitations, pair excitations of quasiparticles through the spin channels, and scales with an effective bandwidth of quasiparticles. This exchange interaction is present only in metallic states.The extended RKKY and the novel exchange interactionscan be ferromagnetic for specific band structures. All of these four exchange interactions can be Cooper-pair interactions.
