Selective disorder in the CuO basal planes of YBa₂Cu₃O_7-y by swift heavy ion induced secondary electrons

Abstract

In situ temperature dependent resistivity, ρ(T) study on c-axis oriented YBa₂Cu₃O_7-y thin films irradiated with 200 MeV Ag ions at 79 K is shown to induce point defects in addition to amorphous ion tracks. Annealing characteristics of these defects indicate that the point defects are basically oxygen disorder selectively created in the CuO basal planes of YBa₂Cu₃O_7-y structure by secondary electrons emanating from the path of 200 MeV Ag ions. These electrons are shown to create defects by inelastic interaction process. Contrary to the general expectation, we show that the superconducting transition temperature, T_c is suppressed at a rate two orders of magnitude faster at extremely low fluences where ion tracks are far apart from each other than at high fluences where tracks tend to overlap. The transition width on the other hand remains unaffected while resistivity shows a large increase at high fluences. At high fluences, a two-step superconducting transition emerged, which indicate the evolution of two types of superconducting regions with distinctly different T_cs.