Atomic structure and composition of the barrier in the modified interface high-Tc Josephson junction studied by transmission electron microscopy

The atomic structure and composition of modified interface junctions which showed reproducible critical current Ic (Ic1σ<8% for 100 junctions) are investigated by transmission electron microscopy. Transmission electron microscopic observations show the existence of a thin barrier (1–2 nm) homogeneously covering the ion milled edge of the base YBa2Cu3Oy film although there is no barrier deposition and annealing process. High-resolution electron microscopy images and energy dispersive x-ray analysis with a spot size of 1 nm indicates that the barrier is a Ba-based perovskite-like structure, (Y1−xCux)BaOy with x<0.5. A thin amorphous layer whose composition deviates from YBa2Cu3Oy is formed due to the preferential sputtering of Cu. The amorphous layer recrystallizes into the nonequilibrium phase (Y1−xCux)BaOy after heating up to the deposition temperature.