  The critical current density Jc in high-Tc superconductors (HTS) often shows
a maximum at field far above the self-field. We study this peak effect(PE) with
the nonlinear I-V response of type-II superconductors and find analytical
equation of Jc in the dependence of filed and temperature. Theis equation is
compared with some experimental data of R-Ba-Cu-O single crystals with fair
agreement.
