Strengthening of reentrant pinning by collective interactions in the peak effect

Since it was first observed about 40 years ago [A. B. Pippard, Proc. R. Soc. A 216, 547 (1953)10.1098/rspa.1953.0040], the peak effect has been the subject of extensive research mainly impelled by the desire to determine its exact mechanisms. Despite these efforts, a consensus on this question has yet to be reached. Experimentally, the peak effect indicates a transition from a depinned vortex phase to a reentrant pinning phase at a high magnetic field. To study the effects of intrinsic pinning on the peak effect, we consider FexNi1-xZr2 superconducting metallic glasses in which the vortex pinning force varies depending on the Fe content and in which a huge peak effect is seen. The results show that the peak effect broadens with decreasing pinning force. Typically, pinning is increased by pinning centers, but here we show that reentrant pinning is due to the strengthening of interactions and collective effects (while decreasing pinning strength).