ON THE APPLICABILITY OF THE CRITICAL STATE MODEL TO THE DESCRIPTION OF ELECTROMAGNETIC PROPERTIES OF HIGH-TC SUPERCONDUCTORS

The frequency dependence of the surface impedance of superconductors have been studied experimentally and theoretically in the radio frequency range. Its essential deviation was found from the linear law predicted by the usual critical state model. The character of this deviation depends qualitatively on the amplitude of the radio wave. We have established the frequency limits of applicability of the traditional critical state model. Results obtained print out an explanation in the frame of the modified model where we take into account the contribution of a dissipative term to the screening current. The value of this is connected with the V-I plot of the superconductor, so it is possible to obtain information about the V-I characteristics by the contactless method.