Extended Power Law Nonlinear Response and Amplitude-Dependent ac Susceptibility of High-T_c Superconductors

We show a nonlinear materials equation of superconductors in the form of an extended power law which can be derived from the Ginzburg-Landau (GL) functional. The critical current J_c and ac susceptibility X are analysed by using this equation, and the puzzling question of the increasing height of the out-of-phase susceptibility peak X''_peak with increasing amplitude h_ac is explained.