Conductance as a function of temperature in the double-exchange model

We have used the Kubo formula to calculate the temperature dependence of th e electrical conductance of the double-exchange Hamiltonian. We average the conductance over a statistical ensemble of clusters, which are obtained by performing Monte Carlo simulations on the classical spin orientation of th e double-exchange Hamiltonian. We find that for electron concentrations big ger than 0.1. the system is metallic at all temperatures. In particular, th ere are not any peaks or changes in slope observed in the temperature depen dence of the resistivity near the magnetic critical temperature. We conclud e that the double-exchange model is not able to explain the metal-to-insula tor transition which experimentally occurs at temperatures near the magneti c critical temperature. [S0163-1829(99)03406-2].