Seramik süperiletkenlerde camsı durum davranışı

Strong non-linear dynamic responses developing due to the magnitude and type of driving current in bulk polycrystalline superconducting YiBa2Cu207_s samples were investigated via the time evolution of the sample voltage, the V - t curves. The evolution of nonlinear V - 1 curves, including several novel types of dynamic changes induced by the transport current, were interpreted mainly by the spatial re-organization of the transport current in a multiply connected network of weak- link structure and glassy state relaxation. In addition, the influence of both the bidirectional square wave current and dc current on the evolution of the V - t curves was studied. In well-defined ranges of amplitudes and periods of driving in current and temperatures, it was found that the non-linear response in V- 1 curves to low frequency driving current reflects itself as pronounced regular sinusoidal- type voltage oscillations. The current-induced regular sinusoidal -type voltage oscillations were interpreted in terms of the defective flow of current-induced self-magnetic flux (SMF) lines in a multiply connected network, semi-elastic coupling between SMF lines, and pinning centers. The oscillating mode was also discussed on the basis of the similarity between the flux dynamics and the charge density waves. The experimental techniques introduced in this study provides a useful tool to observe the time variation of the superconducting order parameter. Keywords: Type-II superconductors, high-rc ceramic superconductors, YiBa2Cu207-s, magnetization, critical current, relaxation, flux dynamics, superconducting order parameter.