Ion-velocity dependence of high-density electronic excitation effects in oxide superconductors

Thin films of EuBa2Cu3O y oxide superconductor have been irradiated with high energy heavy ions (80 MeV I, 125 MeV Br, 1.1 GeV Mo and 3.5 GeV Xe) having same electronic stopping power, S e, in order to investigate the ion-velocity dependence of the electronic excitation effects under the constant electronic energy deposition. Although S e is constant, a strong reduction in the irradiation effect on lattice parameter with increasing ion-velocity is observed in the low ion-velocity region around E ∼ 1 MeV/nucleon, while the ion-velocity dependence is hardly observed in the high ion-velocity region of E > 10 MeV/nucleon. If the observed velocity-dependence is assumed to be due to the change in the fraction of S e contributing to defect creation, the fraction in the low velocity region (E ∼ 0.6 MeV/nucleon) is estimated to be about two times larger than that in the high velocity region (E > 10 MeV/nucleon)