Flux-Line Chain State in BSCCO Superconductors Studied by Two-Sided Decoration

A two-sided Bitter decoration technique has been used to study the vortex chain-Abrikosov lattice state that exists in Bi₂ Sr₂ Ca Cu₂ O₈ superconductors when the applied magnetic field is tilted at a large angle from the c axis. From the vortex patterns formed on opposite a-b plane surfaces, we demonstrate that both chain vortices and Abrikosov vortices are oriented close to the sample c axis. Quantitative analyses on the field and tilt angle dependencies of vortex spacing suggest the coexistence of two sets of vortices: one nearly parallel to the c axis and the other in the a-b plane. The formation of vortex chains observed along the a-b plane is due to the weak attractive interaction between parallel and perpendicular vortices.