No abstract

No abstract

No abstract

No abstract

Studies of the low-field electrodynamics of YBaCuO ceramic superconductors are described. An analytical treatment and a numerical simulation are carried out in the model of pinning and viscous flow of hypervortices in high-Tc superconductors (HTSCs) to find the dependence of the real and imaginary components of the surface impedance on the modulus of a static magnetic field and on the amplitude and frequency of an alternating field. Experimental results are presented on the magnetic-field dependence of the impedance components. The studies were carried out in the frequency range from 30 Hz to 1 kHz and at amplitudes of the alternating component of the field from 0.1 to 10 Oe. It is shown that the critical-state model is applicable to HTSCs in the region of low frequencies and small amplitudes of the alternating component of the field. The model of viscous flow of hypervortices gives a good description of the low-field electrodynamics of HTSCs over a wide range of frequencies and, in particular, predicts the experimentally observed hysteresis of the magnetic-field dependence of the surface impedance.