DISSIPATIVE FLUX MOTION IN YBA2CU3O7-DELTA FILMS - INVESTIGATION BY MEANS OF TRANSPORT-I-V CURVES

The nature of dissipative flux motion in epitaxial YBa2Cu3O7-delta thi n films has been investigated by means of resistivity rho(T, B) and tr ansport current-voltage characteristics E (j, T, B) covering up to 5 o rders of magnitude in voltage for a wide range of temperatures (4.2-85 K) and magnetic fields (0.5-7.0 T). Activation energies U(T, B, j) ha ve been determined in the framework of the collective flux creep theor y. It is shown that U(T, B, j) decreases with increasing temperature, magnetic field and current density. In order to study the influence of a well-defined defect structure, columnar defects have been generated by irradiation with 340 MeV Xe-ions. From a scaling law relating the I-V curves after irradiation with the curves before irradiation it is found that vortices pinned by the columnar defects do not contribute t o dissipation. Due to irradiation the irreversibility line is shifted to higher magnetic fields, indicating its connection to the pinning me chanisms present in the samples.