Effect of non-stoichiometry of high-temperature superconductors of the composition Gd$_{1+x}$Ba$_{2-y}$Cu$_3$O$_{7-\delta}$ on vortex pinning and on the vortex liquid-glass phase transition
Abstract:
High-temperature superconducting film samples of the non-stoichiometric composition Gd$_{1+x}$Ba$_{2-y}$Cu$_3$O$_{7-\delta}$ have been systematically studied. The measured $R(T)$ curves in magnetic fields have demonstrated a sharp change in the nature of pinning with the field, which indicates a possible phase transition of the pinned vortex system from a three-dimensional state to a quasi-two-dimensional one. The vortex structure pinning has been described within the thermally activated flux flow model. The analysis of the dependence of the vortex activation energy $U_0(B)$ on the magnetic field has indicated that the influence of thermal fluctuations on the vortex system in non-stoichiometric high-temperature superconductors Gd$_{1+x}$Ba$_{2-y}$Cu$_3$O$_{7-\delta}$ is smaller than that in stoichiometric superconductors of a similar composition.
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