Recent experimental studies of the flux line lattices in type-11 superconductors are reviewed. All the experiments were performed using the Bitter decoration technique which provides means of direct Observation of static vortex structures at the surface of the superconductor. Various aspects of vortex behaviour that can be studied in decoration experiments are considered, in particular vortex lattice ordering and the effects of pinning and anisotropy on the equilibrium vortex arrangement. New vortex phases, such as vortex chains and oval vortices, which were recently discovered in high-temperature superconductors, are also discussed.

No abstract

No abstract

A vortex structure consisting of vortex chains embedded into the flux-line lattice (FLL) has been observed in YBa&(Cu& "Al") 30& z single crystals using the Bitter decoration technique. This structure formed in magnetic fields applied at a high angle, between 50' and 80', with respect to the c axis. Although the vortex chains -FLL mixture looked similar to the vortex structure observed earlier in the highly anisotropic Bi2Sr&CaCu208+z, its evolution with the tilt angle and the applied field demonstrated that it represents an essentially different vortex state which, unlike Bi2Sr2CaCu208+q, originates from the