Effects of Electron Correlation, Orbital Degeneracy and Jahn-Teller Coupling in Perovskite Manganites.

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  • Motome Yukitoshi
    Department of Physics, Tokyo Institute of Technology, Oh–okayama 2–12–1, Meguro–ku, Tokyo 152–8551
  • Imada Masatoshi
    Institute for Solid State Physics, University of Tokyo, Roppongi 7–22–1, Minato–ku, Tokyo 106–8666

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Roles of Coulomb interaction, orbital degeneracy and Jahn-Teller couplingin double-exchange models are examined for perovskite Mn oxides.We study the undoped insulatoras well as metal-insulator transitions by hole doping, and especiallystrong incoherence of ferromagnetic metal.We derive models whereall the spins are fully polarized in two-dimensional planesas indicated by experimental results, and investigate their ground-state propertiesby the quantum Monte Carlo method.At half filling where the number of eg electronsis one per site on average, the Coulomb interaction opensa Mott gap and induces a staggered orbital ordering.The opening of the gap is, however, substantially slower than the mean-field resultsif the Jahn-Teller coupling is absent.The synergy between the strong correlation and the Jahn-Teller couplinglargely enhances the charge gap amplitude and reproducesrealistic amplitudes and stabilization energyof the Jahn-Teller distortion.Doping of carriers destroysthe orbital ordering stabilized by the Coulomb interaction.The short-ranged orbital correlation is critically enhanced in metalstoward the metal-insulator transition, which should be related to the strong incoherence of charge dynamicsobserved in experiments.Our model, moreover, exhibits a uniform ordering of dx2-y2 orbitals over a wide region of dopingin agreement with experimental indications.

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