Anomalous splitting of the first penetration peak in the local magnetization of Bi2Sr2CaCu2O8+y single crystals

A scanning Hall probe microscope (SHPM) with an effective spatial resolution of ∼1 μm has been used to study the local induction in high quality superconducting Bi2Sr2CaCu2O 8+δ single crystals at high temperatures and low magnetic fields. We observed, for the first time to our knowledge, an anomalous splitting of the peak of first full penetration of magnetic field. We discuss the observed splitting, which is connected to the effects of surface and geometrical barriers on the vortex lattice.