INFLUENCE OF HE ION-BOMBARDMENT AT MEDIUM ENERGIES ON THE VORTEX INSTABILITY AT HIGH-CURRENT DENSITIES OBSERVED IN YBACUO FILMS

Isothermal current-voltage (I-V) characteristics of c-axis oriented YB a2Cu3O7-delta films taken in different external magnetic fields mu(0)H , exhibit voltage jumps at a well defined current density J(T, H) poi nting to a specific instability of the vortex system. Interpreted as L arkin- Ovchinnikov (LO)-instability, this behavior allows to extract t he inelastic scattering time tau(in) of quasiparticles. In the present work, the LO-analysis is applied to study the effect of additional de fects on tau(in). For this purpose, YBa2Cu3O7-delta films were irradia ted at 77 K with increasing fluences Phi of 350 keV He+ ions. The I-V characteristics were determined in the temperature range 45 K < T < 80 K and in magnetic fields pip to 5 Tesla. While J as weld as the supe rconducting transition temperature T-c are significantly decreased by the ion bombardment, the critical vortex velocity as deduced from LO-t heory is much less affected. If the temperature dependence of the extr acted scattering times tau(in) is rescaled by plotting versus the redu ced temperature t = T/T-c(Phi), the results for all ion fluences fall on one common curve within the error bars. This leads to the conclusio n that a universal quasiparticle density n(N)(t) dominates the scatter ing rate 1/tau(in).