Investigation of thermally activated flux flow of YBa 2Cu 3O 7/ PrBa 2Cu 3O 7 superlattices in magnetic fields parallel to the a,b plane

Abstract

YBa 2Cu 3O 7 is a strongly anisotropic 3D material. Our observations of thermally activated flux flow in magnetic fields perpendicular to the a,b plane show that the vortices are 3D-like in this material. Making multilayers of the type YBa 2Cu 3O 7/PrBa 2Cu 3O 7 (YBCO/PrBCO) allows to increase the anisotropy and turn the material into a 2D system. We explore this 3D to 2D transition by investigating the thermally activated flux flow behavior in parallel applied fields. We find the parallel field dependence to be markedly different from the perpendicular dependence. At low fields and in multilayers with relatively thick individual layers we find that the activation is largely field independent. At higher fields we observe a crossover to a power law behaviour similar to what is observed in thick YBCO films. In multilayers with 24Å YBCO layers decoupled by thick PrBCO layers (>> 24Å) we find no broadening of the resistive transition up to 20 Tesla.