Orbital polaron in double-exchange ferromagnets

 
T. L. van den Berg,
 
P. Lombardo,
 
R. Hayn
 

I. M. Frantsevich Institute for Problems of Materials Science of the NAS of Ukraine, Krzhizhanovsky str., 3, Kyiv, 03142, Ukraine
Physical Review B - Maryland, USA: American Physical Society (APS), 2012, #86
http://www.materials.kiev.ua/article/639

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.