First Order Transition of the Vortex Lattice in Disordered Bi-2212 Crystals

Using differential magneto-optical imaging, we address the question of mesoscopic inhomogeneity in underdoped Bi-2212 single crystals. Among other features, it is shown that an anomalous temperature dependence of the penetration field and of the first order transition (FOT) field of the vortex lattice in such crystals can be understood as arising from inhomogeneity. The effect of chemical inhomogeneity and pinning on flux penetration and the FOT is discussed.