Low-energy charge dynamics in   La$_{\text{0.7}}$Ca$_{\text{0.3}}$MnO$_{\text3}$: THz time-domain   spectroscopic studies
  Direct experimental estimations of the low-energy ($1.5\sim10$ meV) complex dielectric constants spectrum and its temperature variation have been investigated for La$_{0.7}$Ca$_{0.3}$MnO$_3$ thin films using terahertz time-domain spectroscopy. At low temperatures, a clear Drude-term emerges. With increasing temperature, the scattering rate increases, while the plasma frequency decreases, derived both from a simple Drude model. Finally, a Drude-term submerges well below the insulator-metal transition temperature. On the basis of the present results, low-energy charge dynamics are discussed. 
N. Kida, M. Hangyo and M. Tonouchi