Suppression and revival of long-range ferromagnetic order in the multiorbital Fermi-Hubbard model

Abstract

By means of dynamical mean-field theory allowing for complete account of SU(2) rotational symmetry of interactions between spin-1/2 particles, we observe a strong effect of suppression of ferromagnetic order in the multiorbital Fermi-Hubbard model in comparison with a widely used restriction to density-density interactions. In the case of orbital degeneracy, we show that the suppression effect is the strongest in the two-orbital model (with effective spin $S_{\rm eff}=1$) and significantly decreases when considering three orbitals ($S_{\rm eff}=3/2$), thus magnetic ordering can effectively revive for the same range of parameters, in agreement with arguments based on vanishing of quantum fluctuations in the limit of classical spins ($S_{\rm eff}\to\infty$). We analyze a connection to the double-exchange model and observe high importance of spin-flip processes there as well.