Anomalous magnetoresistance of ultrathin films of DyBa₂Cu₃O_7-x near the superconductor-insulator transition

An anomalous peak in the magnetoresistance was observed in granular ultrathin films of DyBa₂Cu₃O_7-x whose low-temperature behaviors span the zero-field superconductor-insulator transition. The magnitude of this peak increased with the weakening of the superconductivity of the films. Frustration effects in a Josephson coupled superconducting array are not sufficient to account for the peak. Instead, this unusual behavior may result from an interaction of the carriers with antiferromagnetically ordered Cu²⁺ ions on the copper-oxygen sheets, providing a crucial link between superconductivity and magnetism.