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.

Authors

  • Zhe Sun

  • J. Fraser Douglas

    • University of Colorado at Boulder
  • A. V. Fedorov

    • Lawrence Berkeley National Laboratory
  • Yi-De Chuang

    • Advanced Light Source, Lawrence Berkeley National Laboratory
  • Hong Zheng

    • Argonne National Lab.
    • Materials Science Division, Argonne National Laboratory
  • John Mitchell

    • Materials Science Division, Argonne National Laboratory
    • Argonne National Lab.
    • Argonne National Laboratory
    • Argonne National Lab
  • D. S. Dessau

    • University of Colorado at Boulder