Orbital liquid state in ferromagnetic manganites

We discuss the role of orbital degeneracy in the optical conductivity of pe rovskite manganites in the ferromagnetic metallic phase. Employing an orbit al t-J model we show that the anomalous features of the conductivity spectr um can be well accounted for assuming the existence of an orbital liquid st ate. We further extend our theory to include coupling to dynamical Jahn-Tel ler lattice modes, the result suggesting lattice effects to be present even in the metallic phase of manganites. The theory also is in accordance with the small values of T-linear specific heat found experimentally. (C) 1999 Elsevier Science B.V. All rights reserved.