Microwave measurements of overdoped Y₀.9Ca₀.1Ba₂Cu₃O₇-δ thin films

In the present report we show, for the first time, that a complex order parameter is not just a surface effect, but a bulk: property in overdoped Y₀.9Ca₀.1Ba₂Cu₃O₇- δ thin films. The penetration depth change versus temperature is very well fitted to a complex order parameter of the form Δd_x² - _y² + iδd_xy, where Δ = 14.5 me V and δ = 2meV. This result contrasts our previous results for optimally doped YBCO thin films where a power law for the penetration depth versus temperature was reported, corresponding to a d_x²-_y² - wave order parameter. The penetration depth behavior is accompanied by a rapid reduction of the scattering rate at low temperatures, in contrast with a flattening of this quantity for the optimally doped YBCO films.