Photoemission and x-ray-absorption study of the hole-doped ladder system ${\mathrm{La}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Sr}}_{\mathrm{x}}$${\mathrm{CuO}}_{2.5}$

The hole-doped ladder compound ${\mathrm{La}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Sr}}_{\mathrm{x}}$ ${\mathrm{CuO}}_{2.5}$ has been studied by photoemission and x-ray-absorption spectroscopy. Cluster-model analysis of photoemission spectra and subsequent Hartree-Fock band-structure calculation for ${\mathrm{LaCuO}}_{2.5}$ indicate weak ferromagnetic coupling between the ladders. Changes in the overall electronic structure induced by hole doping are similar to those in ${\mathrm{La}}_{2\mathrm{-}\mathrm{x}}$ ${\mathrm{Sr}}_{\mathrm{x}}$ ${\mathrm{CuO}}_4$. Spectral weight around the Fermi level (${\mathrm{E}}_{\mathrm{F}}$) increases with x and a weak but finite Fermi edge is established at x=0.20.