Effects of interlayer coupling on the dynamic ordering of vortices in high-T-c YBa2CU3O7-delta/PrBa2CU3O7-delta superlattices

We have fabricated and measured transport properties of high-T-c {YBa2Cu3O7 -delta}(8)/{PrBa2Cu3O7-delta(PBCO)}(n) (n = 2, 4, 8) superlattices in order to investigate the effect of interlayer coupling on the vortex dynamics. T he resistive transition was analyzed based on the theory of vortex fluctuat ions such as the Kosterlitz-Thouless vortex-antivortex unbinding transition and two-dimensional (2D) Coulomb gas (CG) analogy of vortices. We have fou nd out that deviation of the sheet resistance curve from the universal one of 2DCG theory increases as the intervening PBCO layer gets thinner, which can be understood as the result of a strengthened interlayer coupling. Meas urements of current-voltage characteristics revealed further evidences of t he vortex-antivortex unbinding transition. From noise measurements, we obse rved that the noise power appeared only in tail parts of resistive transiti on curves and was strongly dependent on both transport current and magnetic field, which implies that the vortex motion is the main source of voltage noise in these specimens. The peak value of noise power showed nonmonotonic dependence on the current, while it was suppressed monotonically with incr easing field. Maximal noise peak power and the corresponding current value increased simultaneously as the PBCO layer got thicker. We could understand these behaviors using the concept of dynamic ordering of vortices, i.e., v ortex motion becomes more independent of vortices in other layers as the in terlayer coupling becomes weaker, thereby enhancing the noise power.