Role of orbital degeneracy in double-exchange systems

We investigate the role of orbital degeneracy in the double-exchange model. In the J_H→∞ limit, an effective generalized “Hubbard” model incorporating orbital pseudospin degrees of freedom is derived. The model possesses an exact solution in one and in infinite dimensions. In one-dimension, the metallic phase off “half-filling” is a Luttinger liquid with pseudospin-charge separation. Using the d=∞ solution for our effective model, we show how many experimental observations for the well-doped (x≃0.3) three-dimensional manganites La_1-xSr_xMnO₃ can be qualitatively explained by invoking the role of orbital degeneracy in the double exchange model.