Vortex instability and hysteresis effects in I– V curves of superconducting Y 1Ba 2Cu 3O 7− δ

Abstract

We have investigated the effect of the current sweep rate (CSR) on the vortex dynamics in superconducting bulk sample of Y 1Ba 2Cu 3O 7− δ . It has been found that the CSR has several dramatic effects on the vortex motion by giving rise enhancement in dissipation as decreasing the CSR, significant time effects, and instabilities in current–voltage ( I– V) curves. The hysteresis loops concerning the I– V curves in both the current-increase and -decrease branches of the forward current region, and also the branches of the reversed current region have been observed together with a gradual diminutive of the hysteresis effects with decreasing the CSR. Due to the field and temperature domain considered, it is also observed that the moving state becomes unstable giving rise some instabilities such as small jumps and steps for both low and moderate current values as a function of CSR. Those anomalies have been discussed in terms of the depinning–pinning correlated to the plastic flow regime together with the disorder in the coupling strength between the superconducting grains, and compared qualitatively to the numerical computer simulations. In addition, for a given field and temperature domain, it has been shown that the CSR together with a relevant current scale is of importance in evolution of the I– V curves and is a useful tool in investigating the details of the vortex dynamics.