Doping dependence of the vortex glass and sublimation transitions in the high-Tc superconductor La2-xSrxCuO4 as determined from macroscopic measurements

Magnetization and ac-susceptibility measurements are used to characterize the mixed phase of the high-temperature cuprate superconductor La2-xSrxCuO4 over a large range of doping (0.075 <= x <= 0.20). The first order vortex lattice phase transition line H-FOT(T), the upper critical field H-c2(T) and the second peak H-sp(T) have been investigated up to high magnetic fields (8 Tesla applied perpendicular to the CuO2 planes). Our results reveal a strong doping dependence of the magnetic phase diagram, which can mainly be explained by the increasing anisotropy with underdoping. Within our interpretation, the. rst order vortex lattice phase transition is due to the sublimation ( rather than melting) of the vortex lattice into a gas of pancake vortices, whereas the second peak is related to the transition to a more disordered vortex glass state.