Electronic bands and optical conductivity of the Dzyaloshinsky-Moriya multiferroic Ba2CuGe2O7
We have measured the reflectivity in the ab plane and along the c axis of a single crystal of the Dzyaloshinsky-Moriya multiferroic Ba2CuGe2O7, from 20 to 300 K and from 700 to 24 000 cm(-1). The resulting optical conductivity sigma(omega) has been compared with the results of calculations of its electronic band structure based on density functional theory (DFT). A broad midinfrared band, which in the ab plane strongly hardens for decreasing temperature, is consistent with d-d transitions of the Cu atom.