Orbital polaron in double-exchange ferromagnets

Abstract

We investigate the spectral properties of the two-orbital Hubbard model, including the pair hopping term, by means of the dynamical mean field method. This Hamiltonian describes materials in which ferromagnetism is realized by the double-exchange mechanism, as for instance manganites, nickelates, or diluted magnetic semiconductors. The spectral function of the unoccupied states is characterized by a specific equidistant three peak structure. We emphasize the importance of the double hopping term on the spectral properties. We show the existence of a ferromagnetic phase due to electron doping near n=1 by the double-exchange mechanism. A quasiparticle excitation at the Fermi energy is found that we attribute to what we will call an orbital polaron. We derive an effective spin-pseudospin Hamiltonian for the two-orbital double-exchange model at n=1 filling to explain the existence and dynamics of this quasiparticle.