Institute for Physics of Microstructures, Russian Academy of Sciences, 603600, Nizhny Novgorod, GSP-105, Russia

Abstract– Superconducting thin films continue to be of interest for passive device application at microwave frequencies, but nonlinear effects may limit their performance. We report a set of experimental data on local third-harmonic generation at microwave frequencies (0.5 GHz) in YBa₂Cu₃O₇ single crystals and thin films, and Nb thin films from 4.2 K to T_c. For local investigations of the nonlinear response a probe with inductive coupling was developed. The third-harmonic power is measured as a function of temperature and dc magnetic field in some places of the sample. The temperature dependence of the third-harmonic signal for YBa₂Cu₃O₇ single crystal and thin film features a number of peaks at temperatures of about 2/3 T_c . There is a strong dependence on an external dc magnetic field for the temperature dependence of the nonlinearity for Nb thin films.

Physics department, Moscow State University, Moscow 119992, Russia.

Abstract - Analytical theory of both the harmonic and subharmonic Shapiro steps on I-V curve of underdamped Josephson junctions in the frame of the resistively shunted junction model has been developed. Domain of applicability of this theory is discussed, and the obtained analitical results are compared with those from numerical simulation.

Department. of Physics, Moscow State University, Moscow 119992, Russia

Abstract – Novel type of phase qubit – the dc superconducting quantum interferometer containing Josephson junctions, which are characterized by a second harmonic in their current-phase relations - was suggested to be realized on the base of high-temperature superconductors. Detailed analysis of the dc interferometer energy versus magnetic field as well as quantum-mechanical behavior of the system are presented. Potentialities of the second harmonic evaluation from the interferometer critical current dependence on magnetic field are also considered. The impact of the second harmonic on the interferometer critical current versus applied magnetic field was analyzed numerically for different values of the normalized interferometer inductance.

Institute for Physics of Microstructures, Russian Academy of Sciences, 603600, Nizhny Novgorod, GSP-105, Russia

Abstract— A problem of nonlinear reflection of electromagnetic wave from a superconductive film was solved assuming a two component s and d superconductive order parameter. The magnitude of re-radiated wave with a frequency equal to three times the frequency of the incident wave (nonlinear response) was derived within the Ginsburg-Landau theory. A temperature dependence of the nonlinear response was analyzed for the different parameters of Ginsburg-Landau theory. A maximum of the nonlinear response at the temperatures of phase transition in between the “pure d<->mixed s and d phase” was predicted for the case of s±d symmetry of order parameter. For the case of s±id symmetry we found that the temperature dependence is gradually increasing close to the phase-transition temperatures.