Polaron coherence condensation as the mechanism for colossal magnetoresistance in layered manganites

Abstract

Angle-resolved photoemission spectroscopy data for the bilayer manganite ${\mathrm{La}}_{1.2}{\mathrm{Sr}}_{1.8}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$ show that, upon lowering the temperature below the Curie point, a coherent polaronic metallic ground state emerges very rapidly with well-defined quasiparticles which track remarkably well the electrical conductivity, consistent with macroscopic transport properties. Our data suggest that the mechanism leading to the insulator-to-metal transition in ${\mathrm{La}}_{1.2}{\mathrm{Sr}}_{1.8}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$ can be regarded as a polaron coherence condensation process acting in concert with the double exchange interaction.