Magneto-optical imaging of vortex lensing in Bi2Sr2CaCu2O8+y

In a highly anisotropic superconductor Bi2Sr2CaCu2O8+y, crossing-lattices state of pancake and Josephson vortices is realized under tilted magnetic fields. In this state, one kind of vortices can drag another, opening a possibility to control the arrangements and motion of vortices in a novel way. We have demonstrated the focusing of pancake vortices in the center of the sample, vortex lensing, by differential magneto-optical imaging in Bi2Sr2CaCu2O8+y. The final arrangement of vortices changes depending on the ramping rate of the in-plane field. Such a behavior is discussed in relation with the competition between the drag force by Josephson vortices and the vortex dome formation due to the surface barrier