Homoepitaxial YBa 2Cu 3O 7− δ SNS junctions with normal layers of YBa 2(Cu 1− xFe x) 3O 7− δ, YBa 2(Cu 1− xZn x) 3O 7− δ, and PrBa 2Cu 3O 7− δ grown on ( [formula omitted])YBa 2Cu 3O 7− δ single crystal substrates

Abstract

We have studied three different homoepitaxial YBa 2Cu 3O 7− δ (YBCO) trilayer SNS junctions grown on (0 0 1) YBCO single crystal substrates with nominally 90 nm thick normal layers of YBa 2(Cu 1− x Fe x ) 3O 7− δ , YBa 2(Cu 1− x Zn x ) 3O 7− δ , and PrBa 2Cu 3O 7− δ (PBCO). Fe-doped YBCO SNS junctions show clear weak link characteristics with a normal Fraunhofer diffraction pattern. The 32×32 μm 2 junction shows a high value of I c R n product, 255 μV, at 6.71 K irrespective of low current density J c=28.3 A/cm 2. On the other hand, Zn-doped YBCO or PBCO SNS junctions shows flux-flow type I–V characteristics. The improvement of I c R n product, 255 μV, of the Fe-doped YBCO SNS junctions comes from high value of R n=0.88 Ω to compensate low value of I c =290 μ A by the improvement of surface morphology of homoepitaxial YBCO SNS structures. The above different device characteristics will be ascribed to the large differences of surface morphology of normal layers or diffusion of Fe and Zn in YBCO layers.