High-Frequency Electrodynamics of Nanostructured Multiband Superconductors

The effect of artificially created 0D and 1D structural defects’ nanostructure formed by implanted dielectric nanoparticles or irradiation defects on microwave properties of high-Tc superconductor films is analysed based on the phenomenological theory for microwave response of type-II superconductors. The surface resistance is calculated for the Meissner and mixed states for such a kind of nanostructured type-II superconductor film. An emergence of nonlinear response caused by the entrance of microwave-induced vortices in the film interior through its edges is also theoretically explored. The obtained results demonstrate that artificial defect nanostructure inside the superconductor can significantly improve its microwave characteristics in both the Meissner states and the mixed ones and increase the range of the linear microwave response. We also present results of experimental studies on microwave properties of high-temperature superconductor (HTS) films with artificial defect nanostructure formed by heavy-ion irradiation. Noticeable decreases of the surface resistance and enhancement of the linear response range at low temperatures are observed for moderately irradiated HTS YBa2Cu3O7−x (YBCO) film exposed to irradiation by 3 MeV Au2+ ions at dose 1011 cm−2. These results are in agreement with the above-discussed phenomenological theory for microwave response of nanostructured superconductors. A theoretical model concerning the new unusual mechanism of the nonlinear radio-frequency (RF) response in multiband superconductors is also presented. This is a mechanism of nonlinearity based on the possible dissociation of Abrikosov’s vortices in multiband superconductors into fractional components under the strong RF current action. We have calculated the RF complex resistivity in two-band superconductors and grounded an emergence of specific peculiarities at critical current density values corresponding to the vortex depinning and dissociation.