Effects of defect morphology on the properties of the vortex system in Bi2Sr2CaCu2O8+δ irradiated with heavy ions -: art. no. 224502

To study the effects of defect morphology on vortex dynamics, reversible magnetization, and e-axis magneroresistance, Bi2Sr2CaCu2O8+delta single crystals are irradiated with heavy-ions; 0.7-GeV Kr-84, 3.5-GeV Xe-136, 3.8-GeV Ta-181, and 3.1-GeV Bi-209. First, defect morphology is investigated by transmission electron microscope (TEM) observations, which reveals that the fluctuation of defect radius along the ion path increases with decreasing the electronic-stopping power for the incident ion S-e. The frequency dependence of the loss-peak temperature, where the imaginary part of ac susceptibility reaches a maximum, shows that the power-law behavior of a Bose-glass transition appears only for the irradiation with [S-e] greater than or similar to 1.9 keV/Angstrom, where [S-e] is the mean value of S-e in the sample. The magnetic-field dependence of reversible magnetization clearly shows the feature of the recoupling of vortices along the c axis only for Ta and Bi irradiations with [S-e] greater than or similar to 3.3 keV/Angstrom. The magnetoresistance along the c axis also reveals that the recoupling of vortices caused by the production of columnar defects takes place when [S-e] greater than or similar to 3.3 keV/Angstrom. The present results demonstrate that the fluctuation in the defect radius along the ion path suppresses the Bose-glass transition and the recoupling of vortices along the c axis.