Inelastic X-ray scattering (Compton) study of La_1.85Sr_0.15CuO₄ - Anisotropic electron momentum distribution

High resolution Compton profiles along two principal symmetry directions (with scattering vector q parallel to [100] and [001]) have been measured from a single crystal of La_1.85Sr_0.15CuO₄ using 58 keV X-rays at a momentum resolution of 0.17 a.u. The measurements are interpreted in terms of highly accurate all-electron computations of the profiles in the parent compound La₂CuO₄ within the local density approximation (LDA) based conventional band-theory framework, assuming that the resulting metallic state is representative of the Sr-doped compound. Although the experimental anisotropy of the profiles, ΔJ = J_[001]-J_[100], and the first and second derivatives of the profiles are in reasonable overall accord with the computations, there are striking discrepancies as well. We suggest that these discrepancies may indicate a substantially larger O 2p character of the doped holes in La₂CuO₄ than implicit in the standard band-theory picture.