Infrared Hall conductivity of Na$_{0.7}$CoO$_2$

Abstract

We report infrared Hall conductivity $σ_{xy}(ω)$ of Na$_{0.7}$CoO$_2$ thin films determined from Faraday rotation angle $θ_{F}$ measurements. $σ_{xy}(ω)$ exhibits two types of hole conduction, Drude and incoherent carriers. The coherent Drude carrier shows a large renormalized mass and Fermi liquid-like behavior of Hall scattering rate, $γ_{H} \sim aT^{2}$. The spectral weight is suppressed and disappears at T = 120K. The incoherent carrier response is centered at mid-IR frequency and shifts to lower energy with increasing T. Infrared Hall constant is positive and almost independent of temperature in sharp contrast with the dc-Hall constant.