Collapse of the peak effect due to ac-induced flux creep in an isotropic vortex system of MgCNi3 single crystals.

In an isotropic vortex system of MgCNi 3 single crystal, we first observed the collapse of the peak effect (PE), which is a sudden increase in the critical current (I c ) near the end of superconductivity. By moving magnetic vortices with dc and ac driving currents, we investigated the vortex dynamics related to the PE. For the dc driving, a sharp peak in I c was observed. As the driving frequency increases, the PE was collapsed and observable flux creep was developed in contrast to the result obtained from the well-studied anisotropic system of NbSe 2 . Because the vortex matter in our experimental situation is isotropic and has large correlation volume without severe deformation by pinning, the mobility of the vortex matter is intrinsically high. From the detailed observation, we are convinced that the PE is definitely a dynamic phenomenon.