Vortex dynamics in columnar-defected YBCO-films

By high-resolution SQUID-magnetometry, we study the influence of columnar defects of field-equivalent density Bφ=1 T on the flux creep in thin YBa2Cu3O7−δ films. At temperatures T*(B,Bφ), the relaxation rates reveal a sharp crossover from a glassy dynamics to a faster algebraic flux creep which disappears at the transition lines Tc(B) to equilibrium superconductivity. As key results we report the effect of defect filling f=B/Bφ on the exponent μ of the glassy vortex dynamics at T