Low Frequency Conductivity Scaling in CaRuO$_3$

We present low frequency conductivity measurements of CaRuO$_3$ thin films using time domain terahertz spectroscopy. The complex conductivity is measured in the frequency range of 200~GHz to 1.4~THz and temperature range of 10~K to 290~K. Below 50~K a Drude-like peak develops which is sufficiently narrow that it is only observable in our frequency window. We also observe a universal scaling of conductivity in the form of $\rm{\sigma_1\omega^{1/2}\propto g(\omega/T)}$ for $1<\rm{\hbar\omega / k_BT<5}$, in agreement with infrared observations of Lee et al.\footnote[1]{Y.S. Lee et al. Phys Rev B {\bf66}, 041104 (2002)} However, our low frequency range allows us to identify deviations from such scaling for $\rm {\hbar\omega /k_BT<1}$.