Thermal conductivity of manganite perovskites: Colossal magnetoresistance as a lattice-dynamics transition

We present the thermal conductivity (kappa) of several manganite perovskite compounds at temperatures 10-350 K and fields up to 6 T. In the metallic phase, kappa behaves as expected for a crystalline solid. In the high-temperature insulating phase, however, d kappa/dT >0, the behavior of an amorphous solid. Unlike amorphous solids, d kappa/dT >0 here is related not to quenched structural disorder but rather to unusually large dynamic lattice distortions accompanying charge transport. Thus, ''colossal magnetoresistance'' in the manganite perovskites is characterized as a transition between regimes of different lattice dynamics.