Dynamical mean-field theory of an Ising double-exchange model with diagonal disorder - art. no. 174409

We present a simplified model for the colossal magnetoresistance in doped m anganites by exactly solving a double-exchange model (with Ising-like local spins) and quenched binary disorder within dynamical mean field theory. We examine the magnetic properties and the electrical and thermal transport. Our solution illustrates three different physical regimes: (i) a weak-disor der regime, where the system acts like a renormalized double-exchange syste m (which is insufficient to describe the behavior in the manganites); (ii) a strong-disorder regime, where the system is described by strong-coupling physics about an insulating phase (which is the most favorable for large ma gnetoresistance); and (iii) a transition region of moderate disorder, where both double-exchange and strong disorder effects are important. We use the thermopower as a stringent test for the applicability of this model to the manganites and find that the model is unable to properly account for the s ign change of the thermopower seen in experiment.