PATH OF MAGNETIC-FLUX LINES THROUGH HIGH-T-C COPPER-OXIDE SUPERCONDUCTORS

A SERIOUS impediment to many potential applications of the high-transition-temperature (high-T-c) copper oxide superconductors is the relative ease with which magnetic flux lines move within these materials, thereby producing finite electrical resistance(1,2). To devise methods for rigidly fixing flux lines in these materials, which is necessary to achieve a truly superconducting (zero resistance) state, requires an understanding of their fundamental properties. In clean, conventional type II superconductors, flux lines or vortices can be modelled well as rigid objects that pass straight through a sample. In the high-T-c materials, however, comparatively short coherence lengths, large anisotropies and large accessible thermal energies lead to more complex and fascinating behaviour, giving for example entangled flux lines and two-dimensional pancake vortices(3-5). Some detail of the vortex lattice has been resolved previously(6-13), although it is not clear how vortices pass through these materials. Here we address this critical issue by simultaneously decorating the positions of flux lines at opposite sides of single-crystal Bi2Sr2CaCu2O8 (BSCCO) high-T-c superconductors using the Bitter technique(14,15). These new data enable us to quantify the wandering of vortices as they pass through the BSCCO high-T-c materials and address the elasticity of the vortex lattice. This information mill be useful for devising effective strategies for pinning flux lints to the crystal lattice.