Direct observation of the vortex structure in high-Tc superconductors in tilted magnetic fields. II. Vortex pinning by twins in YBaCuO single crystals

The high resolution Bitter technique was used for observation of the vortex structure in twinned YBaCuO single crystal in the magnetic field tilted with respect both to the c-axis and to the twin planes. The dominating effect in vortex distribution was strong pinning by twin planes which was seen as an alignment of vortices along twins with approximately two times density higher density than in the bulk. This strong pinning remained unchange for a surprisingly broad interval of tilt angles 0