Oxygen displacement in a $^{107}Ag^{17+}$ ion irradiated $Bi_2Sr_2CaCu_2O_8$ single crystal

We have studied the magnetic field $(H\Vert c)$ dependent rf dissipation $(H_{rf}\Vert fa)$ in an as-grown $Bi_2Sr_2CaCu_2O_8$ single crystal prior to and after irradiation with 250 MeV $^{107}Ag^{17+}$ ions. In a comparison of the responses from the as-grown crystal with an air-annealed crystal, features due to oxygen deficient regions acting as weak links in the former are identified. These features disappear immediately after irradiation of the as-grown crystal. We attribute such behavior to the displacement of oxygen from columnar tracks to deficient regions thus eliminating the weak links. Losses from the same irradiated as-grown crystal stored at 300 K for 60 days show that the features similar but not identical to those observed in the pristine state have reappeared implying that the displaced oxygen is in a metastable configuration in the deficient regions and hence is mobile due to thermal effects even at 300 K.