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

A SERIOUS impediment to many potential applications of the high-transi tion-temperature (high-T-c) copper oxide superconductors is the relati ve ease with which magnetic flux lines move within these materials, th ereby producing finite electrical resistance(1,2). To devise methods f or 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 a s rigid objects that pass straight through a sample. In the high-T-c m aterials, however, comparatively short coherence lengths, large anisot ropies 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 vorti ces pass through these materials. Here we address this critical issue by simultaneously decorating the positions of flux lines at opposite s ides of single-crystal Bi2Sr2CaCu2O8 (BSCCO) high-T-c superconductors using the Bitter technique(14,15). These new data enable us to quantif y the wandering of vortices as they pass through the BSCCO high-T-c ma terials and address the elasticity of the vortex lattice. This informa tion mill be useful for devising effective strategies for pinning flux lints to the crystal lattice.