GROWTH OF THIN CEO2-YBA2CU3O7 SUPERLATTICES

We have grown a series of CeO2-YBaCu3O7 superlattices by pulsed laser deposition. The purpose was to study the growth of an insulator - high temperature superconductor system on a subnanometre scale. This is important for superconducting devices, since the superconducting coherence length is of the order of one to a few nanometres. The scale of the superlattices ranges from a period of about 10 nm down to about 3 nm. The structure of the layers was studied using X-ray diffraction and transmission electron microscopy. We found that superlattices have a coherent, epitaxial structure. The CeO2 follows the Frank - van Merwe growth mode, where the growth proceeds by growing islands about 2 nm thick that coalesce to form a continuous CeO2 layer at an average thickness of 2 nm. We see no evidence of chemical mixing between the YBa2Cu3O7 and CeO2, which implies that they are mutually insoluble at the growth temperature. We have characterized the superconducting properties of the layers using a microwave cavity method at 30 GHz. If the CeO2 layers are thin enough, the superlattices have similar surface resistance and critical temperature as pure YBa2Cu3O7 filMS.