Observation of vortex movement in oxide superconductors by means of the Bitter pattern technique

The high-resolution Bitter pattern technique has been used to observe vortex movement of oxide superconductors, Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 2/ (Bi2212). The Bitter pattern was observed in field-cooled (FC) and zero-field cooled (ZFC) experiments. We also examined vortex movement of the Bi2212 single crystal in which transport current was applied parallel to the c plane, and a dc magnetic field applied normal to the c plane at the Ni decoration. The Ni decoration pattern was observed using a scanning electron microscope (SEM) and an atomic force microscope (AFM). Through observation of the Ni decoration pattern, we can identify vortex movement. The vortices moved into the sample on FC experiment, and the direction of vortex movement was approximately normal to the edge of the sample. We also found the vortex movement in a line under application of transport currents. They moved hopping among pinning centers due to Lorentz force.