Optical studies of charge dynamics in c-axis oriented superconducting MgB2 films

Temperature dependent optical conductivities and DC resistivity of c-axis oriented superconducting (Tc = 39.6 K) MgB2 films (~ 450 nm) have been measured. The normal state ab-plane optical conductivities can be described by the Drude model with a temperature independent Drude plasma frequency of omega_{p,D}=13,600 +/- 100 cm-1 or 1.68 +/- 0.01 eV. The normal state resistivity is fitted by the Bloch-Gruneisen formula with an electron-phonon coupling constant lambda_{tr} = 0.13 +/- 0.02. The optical conductivity spectra below T_c of these films suggest that MgB2 is a multi-gap superconductor.