Lancaster, Passive Microwave Device Applications of High-Temperature Superconductors (Cambridge University Press, Cambridge, 2006) Then, comparing measurements with and without the crystal it is possible to extract the London penetration depth and its anisotropy, quasiparticle conductivity, surface impedance and, when a coexisting magnetic phase is present, even its bulk complex susceptibility. It consists of coupling the crystal to a CPWR, fixing it to the central conductor in a region far form edges, where rf magnetic fields are quite homogeneous. The second approach is suitable for the characterization of single crystals. Relatively low dc fields and rf currents drive the device into a nonlinear regime, allowing us to investigate peculiar features such as those induced by vortex avalanches or weak-link switching. Such CPWRs, not optimal from the point of view of power handling capability, are for this reason suitable to study nonlinear and dissipation mechanisms limiting this property. Analysing the temperature dependence of resonance frequency and quality factor, the London penetration depth and complex impedance were extracted. To study the microwave properties of thin films, CPWRs were obtained from the films themselves by proper patterning. Essentially, we employed two different approaches. Then, we report on the microwave methods we adopted to obtain the results discussed in the second part of the book, all based on the use of coplanar waveguide resonators (CPWRs). In this chapter we provide a brief overview of the main microwave techniques employed for the characterization of superconductors, with a focus on the use of resonant methods.
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