Infrared Faraday measurements on Ba(Fe$_{\mathrm{1-x}}$Co$_{\mathrm{x}}$)$_{2}$As$_{2}$ superconductors

We report infrared Faraday measurements on electron-doped Ba(Fe$_{\mathrm{1-x}}$Co$_{\mathrm{x}}$)$_{2}$As$_{2}$ superconducting films, which are grown by pulsed laser deposition. The complex Faraday angle $\theta_{\mathrm{F}}$ is proportional to the difference of the sample's response to right and left circularly polarized light, making it a highly sensitive tool to probe electronic structure, electron-electron correlations, and magnetic ordering. We measure $\theta _{\mathrm{F}}$ for normal and superconducting states in the 110-1400 meV range at temperatures down to 10K and magnetic fields up to 7T. This work is supported by NSF-DMR1006078.