Y1−xCaxBa2Cu3O7−δ thin films: From phase fluctuations to a complex order parameter Original Research Article

This report presents a study of the temperature dependence of the penetration depth in Y1−xCaxBa2Cu3O7−δ thin films, which shows that a contribution to the order parameter from phase fluctuations in optimally doped samples cannot be excluded, and demonstrates the appearance of an imaginary component in the order parameter in overdoped samples. Measurements were performed using two complementary techniques: the parallel plate resonator (PPR), operated at 10 GHz, and far infrared (FIR) transmission, where the absolute value of the penetration depth can be obtained.