Superlattices of high-temperature superconductors: synthetically modulated structures, critical temperatures and vortex dynamics

We present in this paper an overview of the work that has been performed on hightemperature superconductor superlattices, with a special emphasis on the superconducting properties of YBa2Cu3O7/PrBa2Cu3O7 multilayers. The critical temperature and superconductivity in ultra-thin films, the vortex dynamics, and the field-temperature vortex phase diagram in YBa2Cu3O7/PrBa2Cu3O7 multilayers are studied and compared to bulk behaviour. In particular, the roles of the individual layer thicknesses and the conductivity of the spacer material are studied, as well as the coupling between superconducting layers and the effect of finite multilayer thickness. Comparisons with other systems are made, and an interpretation is proposed for the understanding of superconductivity in ultra-thin oxide films. The field-temperature vortex phase diagram is determined in coupled multilayers and compared to single crystal results. Finally, we discuss the development of novel oxide systems and heterostructures, and the possibilities brought out by new material combinations. 0034-4885/97/121673+49$59.50 c © 1997 IOP Publishing Ltd 1673 1674 J-M Triscone and Ø Fischer