Nonlinear properties of coplanar superconducting YBa2Cu3O7-δ microwave devices in weak magnetic fields

In this work, the nonlinear properties of high-Tc superconducting microwave devices are investigated and the mechanism that limits the power handling capability is derived from the experiment. For this purpose, additional to the rf electromagnetic field, dc magnetic fields are employed as a probe for the analysis of the local maximum rf electromagnetic field. Coplanar microwave resonators which exhibit a characteristic rf current density distribution are manufactured from YBa2Cu3O7-δ thin films on sapphire and LaAlO3 substrates. It is shown that the behaviour of these resonators in dc magnetic fields depends strongly on the vortex distribution in the resonator and, therefore, on the way the magnetic field is established. The experimental results are explained in terms of a model which consistently describes the behaviour in magnetic fields and in zero field. The results are important for the understanding of the mechanism that limits the power handling capability as well as they give a first insight into vortex matter (pinning and mobility) in rf fields. Furthermore, they represent the basis for improvements of the microwave properties of superconducting devices for applications, which is indicated in this work. (orig.)