Millimeter wave surface impedance and far infrared reflectivity of epitaxially grown high Tc thin films

Microwave surface impedance data at 87GHz of epitaxially grown thin films of YBa2Cu3O7-δ prepared in situ by excimer laser ablation, dc sputtering, and thermal coevaporation on SrTiO3, MgO, and LaAlO3 are compared. At 77K the lowest surface resistance values were achieved with laser ablated films on SrTiO3. At 4.2 K and low field levels for all preparation techniques and all substrates nearly the same anomalous high residual surface resistance values occur. Both the microwave and the far infrared reflectivity data at 4.2K are described consistently within the two fluid model indicating a large amount of remaining normal conducting charge carriers.