EVOLUTION OF THE ELECTRONIC-STRUCTURE OF LA2-XSRXCUO4 WITH DOPING DETERMINED BY POSITRON-ANNIHILATION SPECTROSCOPY

We have measured and calculated the electron-positron momentum distrib ution Of La2-xSrxCuO4 samples for Sr concentrations of 0, 0.1, 0.13, a nd 0.2. Measured distributions were obtained at room temperature with high statistical precision, greater than 4X10(8) events, in the Lawren ce Livermore National Laboratory positron-annihilation angular correla tion spectrometer on single-crystal samples fabricated using the trave ling solvent floating zone technique. Corresponding theoretical moment um-density calculations were performed using the linear muffin-tin-orb ital method. The momentum distribution of all samples contained featur es derived from the overlap of the positron distribution with the vale nce electrons. In addition, discontinuities typical of a Fermi surface are seen in the.doped samples. The form and position of these feature s are in general agreement with the Fermi surface and overall momentum distributions as predicted by band theory. However, the evolution of the Fermi surface with doping differed significantly from expectations based on single electron band theories.