Direct observation of vortices in high-Tc superconductors

The structures of vortices inside high-T-c superconductors are now observable using Lorentz microscopy with our newly developed 1-MV field-emission transmission electron microscope, which has the brightest electron beam with the narrowest monochromaticity yet reported. Using this microscope, we identified previously unseen unconventional behaviors of vortices in anisotropic high-T-c superconductors: we distinguished different structures of vortex lines inside high-T-c superconductors, such as vortex lines perpendicular to the layer plane and tilted ones trapped by columnar defects, as different images. We found to our surprise that when the sample temperature decreased below 14 K, the vortices trapped and strongly pinned along tilted columnar defects became perpendicular to the film plane, as if the defects had disappeared. We were also able to clarify the mechanisms of unconventional arrangements, such as the chain state of vortices in YBCO and the chain-lattice state of vortices in Bi-2212, in an inclined magnetic field and also the mechanism of the unexpected chain-vortices image disappearance in Bi-2212. (C) 2003 Elsevier Science B.V. All rights reserved.