Effects of disorder and scaling of optical conductivity in Nd0.5Ca0.5−xBaxMnO3 (x=0 and 0.02) thin films as observed by terahertz time-domain spectroscopy

We have explored the low energy charge dynamics of charge-ordered Nd0.5Ca0.5MnO3 and Ba-doped Nd0.5Ca0.48Ba0.02MnO3 manganite thin films by recording the complex optical spectra using terahertz time-domain spectroscopy. The extracted frequency- and temperature-dependent optical conductivity (σ) and dielectric constant (e1) show distinct features at Neel’s ordering and the charge-ordering temperatures (TN and TCO). We found that the Ba-doping induced cation disorder effects on σ and e1 are more pronounced above TCO, but these effects are subtle in a large temperature region below TCO. Both e1 and σ increase as a function of temperature and form a scaling relationship e1∝σ.