Magnetoresistance anomaly in high-temperature superconducting perovskites

A “stationary point” dividing two regions of the resistive transitions (in one of which the sensitivity of the resistance to magnetic field is low) is observed on the R(T) dependences for polycrystalline samples and monocrystalline films (with a magnetic field orientation parallel to the substrate) of YBa2Cu3Ox measured in different magnetic fields. The position of the stationary point is practically independent of H. These results indicate an extremely weak effect of the magnetic field on the resistance near the temperature Tc and cannot be explained by using conventional concepts concerning fluctuational phenomena in superconductors. The type of the resistive transition in superconducting perovskites is found to be closer to the percolation transition than to an ordinary second-order phase transition. The reason behind the observed peculiarities in the R(T) dependence lies in strong nonuniformities in Tc and in the contribution to the lowering of the resistance from solitary CuO planes displaying fluctuational superconductivity, but not coupled with one another through Josephson interactions.

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