Correlations versus Superfluid Density in La 2 − x Sr x CuO

We have performed muon spin relaxation and low field ac-susceptibility measurements in a series of high quality samples of La 2−x Sr x CuO 4 (x = 0.08 − 0.24) as a function of temperature. Superconductivity is found to co-exist with low temperature spin glass order up to the optimally doped region where the normal state pseudogap also closes. The systematic depletion of the superfluid density with the enhancement of aniferromagnetic correlations with underdoping indicates a competition between antiferromagnetic correlations and superconductivity. Establishing and understanding the phase diagram of the high-T c superconductors (HTS) versus temperature and doping has been one of the major challenges in modern solid state physics. The parent compound La 2 CuO 4 of the first HTS family to be discovered, La 2−x Sr x CuO 4 , is an insulator exhibiting long range antiferromagnetic (AF) order, which is eventually destroyed as carriers are doped into the CuO 2 planes. After passing through a spin glass (SG) state superconductivity emerges near 0.06 holes/planar-Cu-atom and follows an approximately parabolic doping dependence until it disappears at x ≃0.30. Spectroscopic evidence however, indicates that AF correlations do not seize to exist with the emergence 1