Melting of charge/orbital ordered states in Temperature and magnetic-field-dependent optical studies

We investigated the temperature (Formula presented) and the magnetic-field-dependent (Formula presented) optical conductivity spectra of a charge-orbital-ordered manganite (Formula presented) With variation of T and H, large spectral weight changes were observed up to 4.0 eV. These spectral weight changes could be explained using the polaron picture. Interestingly, our results suggested that some local ordered state might remain above the charge ordering temperature, and that the charge/orbital melted state at a high magnetic field (i.e., at (Formula presented) and (Formula presented) should be a three-dimensional ferromagnetic metal. We also investigated the first order phase transition from the charge-orbital- ordered state to ferromagnetic metallic state using the T- and H-dependent dielectric constants (Formula presented) Through the analysis of (Formula presented) using an effective medium approximation, we found that the melting of charge-orbital-ordered states should occur through the percolation of ferromagnetic metal domains.