Abstract
The preparation of a YBa2Cu3O7−x/LaNiO3/YBa2Cu3O7−x sandwich structured film on a LaAlO3 (100) substrate by a sol-gel method was investigated. YBa2Cu3O7−x/LaNiO3/YBa2Cu3O7−x tri-layer heterostructures with different epitaxial characteristics can be deposited by controlling the heat treatment temperature. X-ray diffraction and transmission electron microscopy results show that the bottom YBCO film grows epitaxially on the LaAlO3 substrate along the c axis, and that this epitaxial growth trend is extended to the subsequently deposited LaNiO3 film. For this reason, the LaNiO3 film also grows epitaxially along the c axis. Furthermore, this epitaxial growth trend is extended to the top YBa2Cu3O7−x film, yielding YBa2Cu3O7−x/LaNiO3/YBa2Cu3O7−x tri-layer heterostructures with epitaxial growth characteristics along the c axis, which enables both the bottom and top YBa2Cu3O7−x layers to possess superconducting abilities.
Highlights
The traditional Josephson junction is composed of a sandwich structured superconductor, insulator and superconductor (SIS); this junction requires the thickness of the insulating layer to be similar to the coherence length of the superconducting layers
The coherence length is rather short in high-temperature oxide superconductors, such as YBa2 Cu3 O7−x (YBCO), which has a length of ξ c
If the middle I layer is replaced by an N layer with metallic conductivity (i.e., superconductor normal superconductor (SNS) structure), the superconducting electron pair, due to the large proximity effect at the interface of a high-temperature superconductor and a conducting layer [1], can pass through the N layer with a thickness of more than 10 nm, which is much farther than the coherence length of the superconductor
Summary
The traditional Josephson junction is composed of a sandwich structured superconductor, insulator and superconductor (SIS); this junction requires the thickness of the insulating layer to be similar to the coherence length of the superconducting layers. If the middle I (insulator) layer is replaced by an N (normal) layer with metallic conductivity (i.e., superconductor normal superconductor (SNS) structure), the superconducting electron pair, due to the large proximity effect at the interface of a high-temperature superconductor and a conducting layer [1], can pass through the N layer with a thickness of more than 10 nm, which is much farther than the coherence length of the superconductor. The SNS structure can be deposited more and various SNS structures have been developed, such as YBCO/La2−x Srx CuO4 (20 nm)/YBCO [2], YBCO/CaRuO3. Studies concerning SNS sandwich structures are considered significant for the preparation of Josephson junctions
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