The pulse-characteristic of thin YBa_2Cu_3O_7 films at high power densities is analysed in terms of an electronic instability as predicted by the theory of Larkin-Ovchinnikov. The critical flux-flow velocity and the resulting inelastic scattering rate of the quasiparticles τ_m are determined as a function of temperature and magnetic induction via two different methods, i.e. by the onset of a peak in the voltage-versus-time characteristic and the theoretical fit of the current-voltage characteristic. The difference between the both values can be ascribed to a slight increase in temperature during the measurement. The results are discussed in terms of the existing theories and literature values obtained via other experimental techniques.
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