Current-driven vortex dynamics in untwinned YBa₂Cu₃O₇ superconducting single crystals

Abstract

Current-driven vortex dynamics of type-II superconductors in the weak-pinning limit is investigated by quantitatively studying the current-dependent vortex dissipation of an untwinned YBa2Cu3O7single crystal. For applied current densities (J) substantially larger than the critical current density (JC), non-linear resistive peaks appear below the thermodynamic first-order vortex-lattice melting transition temperature (TM), in contrast to the resistive hysteresis in the low-current limit (J < JC). These resistive peaks are quantitatively analysed in terms of the current-driven coherent and plastic motion of vortex bundles in the vortex-solid phase, and the non-linear current-voltage characteristics are found to be consistent with the collecive flux-creep model. The effects of high-density random point defects on the vortex dynamics are also investigated via proton irradiation of the same crystal. Neither resistive hysteresis over a wide range of currents and temperatures, despite theoretical predictions of much larger JC-values for the given experimental variables. This finding suggests that the vortex-glass phase, a theoretically proposed low-temperature vortex state which is stabilized by point disorder and has a vanishing resistivity, may become unstable under applied currents significantly smaller than the theoretically predicted JC. More investigation appears necessary in order to resolve this puzzling issue.