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

Small Drude weight D together with small specific heat coefficient γ observed in the ferromagnetic phase of R_1-xA_xMnO₃ (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 e_g orbitals such as 3x² - r² and 3y² - r² symmetries may lead to the critical exponents of D ∞ δ^u and γ ∞ δ^v with u = 3/2 and v = 0. The result agrees with the experimental indications.