Vortex imaging with varying temperature revealed by SHPM on Bi₂Sr₂CaCu₂O_8+y

Scanning Hall probe microscopy with an effective spatial resolution of ∼1 μm has been used to investigate the vortex structures in superconducting Bi₂Sr₂CaCu₂O_8+δ single crystals in the temperature range 77.3-81.3 K and zero applied field (in the presence of the earth field). The vortex images were obtained in real time mode as the temperature increased slowly for 3.36 h. At 77.3 K, the vortices were arranged in a chain structure. With the increase of the temperature, two jumps in the vortex array occur at 77.3 K, immediately when the temperature starts to rise, and at 79.2 K with a good stability between jumps. The second jump is accompanied by the jump in the average magnetic induction when bundles of 4-5 additional vortices enter the scanning area and the vortex array get disordered. These directly visualized transitions in the vortex lattice are consistent with a vortex creep over the surface barriers at high temperatures. A short movie is presented