Study of Residual Absorption of High-Tc Thin Films by Means of Photothermal Interference Spectroscopy

Results of direct absorptivity measurements at ω=0.89 THz of thin films belonging to three different families of HTc compounds are reported. In all samples a significant decrease of absorption below T, with nonzero values at T< unpaired electrons or pairs with a binding energy lower than 0.89 THz in CuO planes. In addition, a considerable rise of the absorptivity for T < 30 K was observed in YBa2Cu3O7−x samples.