A local metallic state in globally insulating La$_{1.24}$Sr$_{1.76}$Mn$_{2}$O$_{7}$ well above the metal-insulator transition
ORAL
Abstract
La$_{2-2x}$Sr$_{1+2x}$Mn$_{2}$O$_{7}$ is a typical colossal magnetoresistive oxide, and it shows a drastic transition from a low-temperature metal to a high-temperature insulator at 120K -160K. The famous CMR ( colossal magnetoresistive) effect usually accompanies the metal-insulator transition. Using angle-resolved photoemission spectroscopy (ARPES) we studied the electronic structure of a bi-layer manganite compound La$_{2-2x}$Sr$_{1+2x}$Mn$_{2}$O$_{7}$ (x=0.38). We found that in the insulating state there remain local metallic regions up to a very high temperature. In these metallic regions, the electronic behavior has minimal change with temperature. Our data indicate that the metal-insulator transition is a new type and an ``emergent'' phenomenon driven by the phase separation and percolation effect. The CMR effect can also be understood in the framework of the phase separation and percolation effect.
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