Vortex gliding between Cu–O planes in an anisotropic high temperature superconductor (abstract)

Abstract

The magnetooptical technique was used to directly observe the magnetic flux penetration in single crystals of the La–Sr–Cu–O superconductor. The large size of the crystals (several millimeters along the three axes) allows for observations to be made along the different crystalline orientations. In a previous study, we reported on direct measurements of critical currents and the dependence of their anisotropy on the amount of Sr doping. When looking at the behavior of vortices which are parallel to the Cu–O planes, we observed that the roughness of the flux fronts was greatly magnified for the highly anisotropic samples. This suggested that the vortices were moving between the planes, as if they were in independent channels. In this communication, we report on observations made when an additional field component is applied along the c axis. Our experiments show that this additional component strongly suppresses the vortex penetration, drastically reducing the apparent anisotropy of the critical currents. We argue that this behavior is consistent with a picture in which the vortices easily move (‘‘glide’’) between the Cu–O planes, and only feel the pinning potential when they are tilted by the additional field component, and thus forced to ‘‘puncture’’ the planes.