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 po larization modulation technique is used to measure simultaneously Faraday r otation and circular dichroism in thin metal films. These two quantities de termine the complex ac Hall conductivity. This technique is applied to stud y 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 omega(H) is consistent with band theory predictions. We report a measurement of the MIR Hall scattering rate gamma(H) which is significantly lower than that derived from Drude an alysis of zero magnetic field MIR transmission measurements. This differenc e is qualitatively explained in terms of the anisotropy of the Fermi surfac e in Au and Cu.