Coherent transition induced by Sr doping on the YBa2Cu3O7-δ single crystal magnetoconductivity

We have studied by magnetoresistivity measurements the influence of the low Sr chemical doping on the conductivity thermodynamic fluctuation regimes (TFR) of a YBa1.98Sr0.02Cu3O7-(delta) single crystal. The low-current and low-frequency resistivity, rho(T,H) measurements were performed in a PPMS while DC magnetic fields up to 50kOe were simultaneously applied perpendicular to the ab plane of the single crystal and to the measurement current density. The d rho(T,H)/dT data shows that the superconducting transition of the sample occur is two stages that corresponds to the signature of a granular superconductor. At this scenario is possible to define two critical temperature transitions T-C(H) and T-C0(IH) [T-C(H) > T-C0(H)]. At T-C(H) the superconductivity sets in within the grains and at T-C0 (H) a coherent transition takes place and a long-range superconducting order takes place over the whole sample. Special attention is reserved to the paracoherent region [T-C0(H)<= T<T-C(H)] of the rho(T,H) data. The field and the temperature dependence of the paracoherent TFR behavior is characterized by a power law represented by a critical exponent S-o approximate to 3. This exponent is an indicative that the coherence transition of the sample belongs to the 3D-XY universality class with relevant disorder that probably is associated to the low Sr doping.