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Optical conductivity of colossal magnetorestistance compounds: Role of orbital degeneracy in the ferromagnetic phase

Peter Horsch·Janez Jaklic·Frank Mack
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Abstract

Recent optical conductivity $σ(ω)$ experiments have revealed an anomalous spectral distribution in the ferromagnetic phase of the perovskite system $La_{1-x}Sr_xMnO_3$. Using finite temperature diagonalization techniques we investigate $σ(ω)$ for a model that contains only the $e_g$-orbital degrees of freedom. Due to strong correlations the orbital model appears as a generalized t-J model with anisotopic interactions and 3-site hopping. In the orbital t-J model $σ(ω)$ is characterized by a broad incoherent spectrum with increasing intensity as temperature is lowered, and a Drude peak with small weight, consistent with experiment. Our calculations for two-dimensional systems, which may have some particular relevance for the double-layer manganites, show that the scattering from orbital fluctuations can explain the order of magnitude of the incoherent part of $σ(ω)$ in the low temperature ferromagnetic phase. Moreover orbital correlation functions are studied and it is shown that $x^2$-$y^2$ orbital order is prefered in the doped planar model at low temperature.

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Peter Horsch, Janez Jaklic, Frank Mack. 1998-07-17. Optical conductivity of colossal magnetorestistance compounds: Role of orbital degeneracy in the ferromagnetic phase. https://doi.org/10.1103/physrevb.59.6217

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