Optical properties of MgCNi3 in the normal state

We present the optical reflectance and conductivity spectra for nonoxide antiperovskite superconductor MgCNi3 at different temperatures. The reflectance drops gradually over a large energy scale up to 33 000 cm(-1), with the presence of several wiggles. The reflectance has slight temperature dependence at low frequency but becomes temperature independent at high frequency. The optical conductivity shows a Drude response at low frequencies and four broad absorption features in the frequency range from 600 to 33 000 cm(-1). We illustrate that those features can be well understood from the intra- and interband transitions between different components of Ni 3d bands which are hybridized with C 2p bands. There is a good agreement between our experimental data and the first-principles band structure calculations.