Defect production in oxide superconductor irradiated with high-energy heavy ions

Ishikawa, Norito   

In this study, resistivity change as a function of ion-fluence has been measured in-situ for an oxide superconductor irradiated with high-energy heavy ions at low temperature in order to elucidate a mechanism of defect production due to high-density electronic excitation. The velocity effect appeared in the electronic stopping power (Se) dependence has been investigated in detail over a wide range of energy and mass of irradiating ions. Oxide superconductor EuBa2Cu3Oy (EBCO) thin films were irradiated at low temperature (100K) with various heavy ions in the energy range of 90 MeV-3.84 GeV, where defect production due to high-density electronic energy deposition is expected. The electrical resistivity were measured in-situ at 100 K. The shape of resistivity-fluence curves varies depending on the electronic stopping power. The resistivity-fluence curves can be reasonably interpreted by assuming the formation of columnar defects (ion-tracks). When Se is low, the resistivity increase as a function of ion-fluence exhibits a saturating behavior, suggesting that each columnar defect has the resistivity at saturation. When Se is high the resistivity increase as a function of ion-fluence shows an exponential increase, suggesting that each columnar defect has the resistivity much higher than that of the matrix. All these results can be consistently interpreted by assuming the accumulation of randomly distributed parallel columnar defects with relatively high resistivity and finite diameter (D).