Fabrication of HTS ramp-edge-type Josephson junctions and SQUIDs using various YBCO-derivatives as barrier materials

Abstract

New barrier materials have been tried to be used for fabrication of ramp-edge-type Josephson junctions (JJs) and SQUIDs in which La0.1Er0.95Ba1.95Cu3O y and SmBa2Cu3O y are used as counter- and base-electrodes, respectively. The derivatives having the YBCO-type structure with a variety of lattice size, Al0.5Sr2Y0.5Ca0.5Cu2.4Zn0.1O y , Mo0.5BaSrPr0.5Yb0.5Cu2.4Zn0.1O y , Yb0.9La0.2Ba1.9Cu3O y , Pr1.4Ba1.6Cu2.6Ga0.4O y , La1.5Ba1.5Cu3O y and TaBa2LaCu2O y were examined. The structure and composition around the barrier region were investigated using an analytical transmission electron microscope for a sample prepared using the Yb0.9La0.2Ba1.9Cu3O y barrier material. It was suggested that an oxygen-deficient perovskite phase exhibiting metallic conduction was crystallized in the barrier region. When TaBa2LaCu2O y was used, large I c R n ’s around 200 μV and SQUID modulation voltages larger than 40 μV were observed. The attained large R n in the JJs prepared using TaBa2LaCu2O y might be attributed to suppression of metallic conduction due to appreciable Ta substitution for Cu in the barrier region.