THERMALLY ACTIVATED FLUX-FLOW IN EPITAXIALLY GROWN YBA2(CU1-XZNX)3O7 THIN FILMS

The influence of Zn-impurity atoms on the superconducting critical temperature T(c), the resistive transitions in magnetic fields rho-ab(B,T) and the critical current density j(c)ab(B,T) of epitaxially grown, c-axis oriented YBa2(Cu1-xZnx)3O7 films is reported. For very small concentrations x less-than-or-equal-to 0.005 we observe a narrowing of the resistive transitions which leads to a crossing of the depinning lines and corresponds to an enhancement of the average activation energy <U> by a factor of two. The pinning effectivity of the Zn-dopant atoms can also be deduced from an enhancement of j(c)ab(B,T)/j(c)ab(0,T) in large magnetic fields B greater-than-or-equal-to 6T and characteristic features in the angular dependence of j(c)ab(B,T,phi) where phi is the angle between the external field B and the c-axis.