Visualization and control of vortex chains in highly anisotropic superconductors

We report the evolution of the vortex state under tilted fields in anisotropic superconductors. Both in highly anisotropic Bi2Sr2CaCu2O8+y and moderately anisotropic underdoped YBa2Cu3O7−δ, vortex chains coexisting with vortex lattices are observed under tilted fields. Despite the similarity of the vortex states, we believe that the state realized in Bi2Sr2CaCu2O8+y and underdoped YBa2Cu3O7−δ are different considering the recent theoretical studies. We visualize the vortex chains in Bi2Sr2CaCu2O8+y using the magneto-optical technique, and demonstrate their controllability by the in-plane field. We also demonstrate the lensing effect of vortices in Bi2Sr2CaCu2O8+y by micro-Hall probe magnetometry and by direct visualization using magneto-optical imaging.