On the Nature of Microwave Response of the Resonator with a Thin FeSe_1-x Te_x Film Near Critical Temperature

Earlier, the authors found a feature in the form of a nonmonotonicity at T < T_c in the temperature dependence of the Q-factor of a cavity resonator with the H₀₁₁ mode, when the FeSe_1-xTe_x superconductor thin film is perpendicular to the microwave magnetic field of the resonator. In this paper, it has been shown experimentally that this nonmonotonicity is absent when the film is parallel to the magnetic field. In both cases, the film is located inside the resonator. Analysis of the temperature dependence of the Q-factor of the resonator with the film in comparison with the results of solving the model electrodynamic problem confirms the conclusion that the nature of the observed feature is due to a change in the orientation and distribution of the microwave magnetic field in the film as the temperature is raised to T ≤ T_c. Obviously, the conclusions drawn are of a general nature and do not depend on the kind of type-II superconductor, the thin film of which is located in the resonator.