One-dimensional spin-orbital model perturbed by Hund coupling

The one-dimensional spin-orbital model perturbed by Hund coupling is studied by renormalization group and bosonization methods. The Hund coupling breaks the SU(4) spin-orbital symmetry into SU(2)(spin) x U(1)(orbital) at weak coupling fixed point. The one-loop renormalization group analysis shows that the Hund coupling is relevant irrespective of Coulomb repulsion. When Coulomb repulsion is larger than Hund coupling, the spin-orbital physics in strong coupling regime is described by SO(6) Gross-Neveu model, where the spin and orbital excitations are gapped. When the Hund coupling is much larger than the Coulomb repulsion, the strong coupling regime is described by the two coupled SO(3)(spin) x SO(3)(orbital) Gross-Neveu model, where again the spin and orbital excitations are gapped. (C) 2003 Elsevier Science B.V. All rights reserved.