Effect of point-like disorder on the vortex phase diagram in Bi ₂Sr₂CaCu₂O_8-δ in oblique field

The phase diagram of vortex matter in the layered superconductor Bi ₂Sr₂CaCu₂O_8-δ exposed to a magnetic field oblique to the crystalline c-axis contains two first order transition (FOT) lines [1]. The first, H_FOT^m, separates the vortex solid from the vortex liquid, the second, H_FOT ^ct, separates the combined lattice state in the vortex solid from a tilted lattice state. The angular dependence of H_FOT^m in the tilted lattice region follows the anisotropic Ginzburg-Landau model [2], allowing for the determination of the anisotropy factor γ_eff and the contribution of magnetic coupling to the mutual interaction of "pancake" vortices in the crossed lattice limit. The later parameter is directly related to the in-plane penetration depth λ_ab. We investigate the evolution of the phase diagram of Bi₂Sr ₂CaCu₂O_8-δ in oblique fields with point-like disorder, introduced by irradiation with 2.3 MeV electrons. Apart from the depression of T_c, point-like disorder induces an increase of γ_eff and a depression of the superfluid density.