DOUBLE AND TRIPLE PEAKS IN THE AC LOSSES OF SOME SUPERCONDUCTORS

We measure transverse a.c. losses of <<dirty>>, fully oxygenated untwi nned YBa2Cu3O7-delta single crystals and 2H-NbSe2 single crystals usin g a low-frequency pendulum oscillator. The data constitute evidence fo r a peak effect of the critical current as a function of the temperatu re in these compounds. The existence of the peak effect explains some complex peak structures in the losses observed in <<dirty>> samples of moderately anisotropic three-dimensional superconductors.