Barrier structure of ramp-edge-type Josephson junction made of La-doped ErBCO and SmBCO electrodes

Highlights: • The structure of the barrier of ramp-edge-type Josephson junction using La-doped ErBCO and SmBCO was investigated by means of transmission electron microscope (TEM). • The image of high-angle annular dark-field scanning TEM (HAADF-STEM) for the barrier indicated that about 1.5-nm-thick barrier homogeneously formed and the ordered structure of the triple perovskite was lost. • Using an energy dispersive X-ray analyzer, the composition at the barrier region was estimated to be Ba:La:Sm:Er:Cu = 23:1:25:10:41. • It was found that significant concentration of Sm occurred at the barrier region. • The formation mechanism of the barrier is discussed on the basis of the fabrication process. - Abstract: We fabricated SQUIDs containing ramp-edge-type Josephson junctions using La-doped ErBCO and SmBCO. The structure of the barrier was investigated by means of transmission electron microscope (TEM). The sample piece for the observation was picked up from a chip exhibiting moderate junction characteristics as DC SQUID at 77 K. The image of high-angle annular dark-field scanning TEM (HAADF-STEM) for the barrier indicated that about 1.5-nm-thick barrier homogeneously formed and the ordered structure of the triple perovskite was lost. Using an energy dispersive X-ray analyzer, the composition at the barrier region was estimated to be Ba:La:Sm:Er:Cu = 23:1:25:10:41. It was found that significant concentration of Sm occurred at the barrier region. The formation mechanism of the barrier is discussed on the basis of the fabrication process and the obtained results.