A new interpretation of the glass-liquid transition of pinned fluxoids in high-T_c superconductors

The present paper proposes a possibility that the transitions between the vortex glass state and the vortex liquid state, which have been observed by the resistive measurements in high-T_c cuprate superconductors, can be interpreted as the thermal-fluctuation-induced percolative transitions of pinned fluxoids. Since weaker flux-pinning centers become successively ineffective due to thermal agitation as the temperature increases, this kind of percolative transition occurs when a narrow channel of unpinned fluxoids penetrates throughout the whole specimen, and hence the flux flow begins to occur through the channel of unpinned fluxoids, where the long range order among fluxoids recovers. The results of computer simulation on the motion of pinned fluxoids support strongly the present mechanism. The present theoretical expression for the scaled master curves of the induced electric field versus the transport current density shows good agreement with existing observed data. The relations of the transition temperature and the scaling exponents to the flux-pinning characteristics are also discussed.