NONLINEAR-INTERACTION OF A TRANSPORT CURRENT WITH AN ELECTROMAGNETIC-WAVE IN HIGH-TC CERAMICS

We have studied theoretically and experimentally a non-linear interaction of a radio wave with a transport current in high-T(c) ceramics in the critical state. It was established that for currents I lower than the critical value I(c) the dependence of the surface impedance of a sample on a transport current is connected with the dependence of the critical current density on the self-magnetic field of a current. When a sample transits to the resistive state and the longitudinal electric field appears, the mentioned interaction leads to sharp decreasing of screening currents. Accordingly, the AC field penetration depth increases. The real part of the surface resistance, as a function of the current I, has a maximum in the region near I almost-equal-to I(c). If the frequency of a radio wave increases, the position of this maximum is displaced to the region of higher currents. We should like to note that it is impossible to explain an observed phenomenon if one considers ceramic media in the resistive state on the basis of the usual skin effect in normal metal.