Nano-structured defects in an oxide superconductor induced by Au and Fe ion irradiation

Long columnar nano-defects were formed in a Bi₂Sr ₂CaCu₂O_x (Bi2212) single crystal irradiated by 230 MeV Au and 180 MeV Fe ions. As expected, the width of the columnar defects induced by the heavy Au ion irradiation gradually decreased with the loss of ion energy in the target along the ion trace. However, in the case of irradiation by the lighter Fe ions, the width of the columnar defects remained almost constant along the ion trace. The conditions required for producing the same type of damage morphology in the same target are very different for the two types of ions, strongly depending on the ion momentum, and hence mass. The relationships between the ion energy and the columnar defect size produced by the two types of irradiation are discussed quantitatively. The relationships are found to be useful for predicting the diameters and distribution of the columnar defects formed by ion irradiation.