Phase diagram of Josephson vortices in Bi-2212-doping dependence

We have studied a magnetic phase diagram of Josephson vortices in slightly (Tc = 86.0 K) and moderately (Tc = 82.5 K) over-doped Bi2Sr2CaCu2O8+δ single crystals by measuring a Josephson-vortex flow resistance. Doping of this range shows a significant change in the lower boundary of the 3D-ordered vortex phase, which was confirmed by the periodic oscillations, and a weak one in the upper boundary, which exists at about 50 kOe at higher temperatures and above 70 kOe at lower temperatures than 30 K in both samples. Above this boundary, the flow resistance shows a different behavior, which may be related to the strength of the interlayer coupling along the c-axis, and to the excitation/annihilation of pancake vortex pairs thermally and magnetically.