Suppressed Coherence due to Orbital Correlations in the Ferromagnetically Ordered Metallic Phase of Mn Compounds

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Small Drude weight D together with small specific heat coefficient γ observed in the ferromagnetic phase of R₁₋ₓAₓMnO₃ (R=La, Pr, Nd, Sm; A=Ca, Sr, Ba) are analyzed in terms of a proximity effect of the Mott insulator. The scaling theory for the metal-insulator transition with the critical enhancement of orbital correlations toward the staggered ordering of two eg orbitals such as 3x²-r² and 3y²-r² symmetries may lead to the critical exponents of D ∝ δᵘ and γ∝ δᵛ with u=3/2 and v=0. The result agrees with the experimental indications.