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The one- and two-orbital double-exchange models for manganites are studiedusing Monte Carlo computational techniques in the presence of a robustelectron-phonon coupling (but neglecting the antiferromagnetic exchange $J_{\rmAF}$ between the localized spins). The focus in this effort is on the analysisof charge transport. Our results for the one-orbital case confirm and extendprevious recent investigations that showed the presence of robust peaks in theresistivity vs. temperature curves for this model. Quenched disordersubstantially enhances the magnitude of the effect, while magnetic fieldsdrastically reduce the resistivity. A simple picture for the origin of theseresults is presented. It is also shown that even for the case of just oneelectron, the resistance curves present metallic and insulating regions byvarying the temperature, as it occurs at finite electronic density. Moreover,in the present study these investigations are extended to the more realistictwo-orbital model for manganites. The transport results for this model showlarge peaks in the resistivity vs. temperature curves, located at approximatelythe Curie temperature, and with associated large magnetoresistance factors.Overall, the magnitude and shape of the effects discussed here closely resembleexperiments for materials such as $\rm La_{0.70} Ca_{0.30} Mn O_{3}$, and theyare in qualitative agreement with the current predominant theoretical view thatcompetition between a metal and an insulator, enhanced by quenched disorder, iscrucial to understand the colossal magnetoresistance (CMR) phenomenon.Comment: 15 pages, 18 figure

Colossal magnetoresistance observed in Monte Carlo simulations of the one- and two-orbital models for manganites