Anisotropic optical signatures of orbital and charge ordering in Bi1-xCaxMnO3

We present a spectroscopic ellipsometry study of the optical anisotropies at energies above and below a crossing point at approximate to 12 eV in the optical conductivity of Bi1-xCaxMnO3 crystals. Below T-co, we observe a sudden increase of the low-frequency dielectric function, reflecting charge ordering. Moreover, we find a gradual development in the high-frequency dielectric function, primarily influenced by orbital effects, which suggest that fluctuations associated with short-range orbital ordering precede charge ordering.