Doping dependence of the vortex glass and sublimation transitions in the high-$T_{c}$ superconductor La$_{2-x}$Sr$_{x}$CuO$_{4}$ as determined from macroscopic measurements

摘要

Magnetization and ac-susceptibility measurements are used to characterize themixed phase of the high-temperature cuprate superconductorLa$_{2-x}$Sr$_{x}$CuO$_{4}$ over a large range of doping (0.075 $\leq x\leq$0.20). The first order vortex lattice phase transition line $H_{FOT}(T)$, theupper critical field $H_{c2}(T)$ and the second peak $H_{sp}(T)$ have beeninvestigated up to high magnetic fields (8 Tesla applied perpendicular to the$CuO_2$ planes). Our results reveal a strong doping dependence of the magneticphase diagram, which can mainly be explained by the increasing anisotropy withunderdoping. Within our interpretation, the first order vortex lattice phasetransition is due to the sublimation (rather than melting) of the vortexlattice into a gas of pancake vortices, whereas the second peak is related tothe transition to a more disordered vortex glass state.