Enhanced Kosterlitz-Thouless transition in YBa2Cu3O7-x/PrBa2Cu3O7-x multilayers as a measure of two-dimensionality

We have observed enhanced Kosterlitz-Thouless transitions in multilayers composed of YBa2Cu3O7-x with a thickness of two and four unit cells, separated by PrBa2Cu3O7-x sufficient to isolate them from one another. The parameter τKT=(Tc0-TKT)/Tc0 is up to an order of magnitude larger than in single crystals or in films, showing that two-dimensional behavior is approached more closely in the multilayers. The fact that the enhancement of two-dimensionality is accompanied by a lowering of Tc0 demonstrates the importance of interlayer coupling.