Resistivity of Mixed-Phase Manganites

The resistivity ${\rho }_{\mathrm{dc}}$ of manganites is studied using a random resistor-network, based on phase separation between metallic and insulating domains. When percolation occurs, both as chemical composition or temperature vary, results in good agreement with experiments are obtained. Similar conclusions are reached using quantum calculations and microscopic considerations. Above the Curie temperature, it is argued that ferromagnetic clusters should exist in Mn oxides. Small magnetic fields induce large ${\rho }_{\mathrm{dc}}$ changes and a bad-metal state with (disconnected) insulating domains.