Midinfrared Hall effect in thin-film metals: Probing the Fermi surface anisotropy in Au and Cu

A sensitive midinfrared (MIR, 900--1100 cm^-1, 112--136 meV) photoelastic polarization modulation technique is used to measure simultaneously Faraday rotation and circular dichroism in thin metal films. These two quantities determine the complex ac Hall conductivity. This technique is applied to study Au and Cu thin films at temperatures in the range (300 K >T > 20 K), and magnetic fields up to 8 T. The Hall frequency ωH is consistent with band theory predictions. We report a measurement of the MIR Hall scattering rate γH which is significantly lower than that derived from Drude analysis of zero magnetic field MIR transmission measurements. This difference is qualitatively explained in terms of the anisotropy of the Fermi surface in Au and Cu.