Inelastic X-ray scattering (Compton) study of La1.85Sr0.15CuO4 - anisotropic electron momentum distribution

High resolution Compton profiles along two principal symmetry directions (w ith scattering vector q parallel to [100] and [001]) have been measured fro m a single crystal of La1.85Sr0.15CuO4 using 58 keV X-rays at a momentum re solution of 0.17 a.u. The measurements are interpreted in terms of highly a ccurate all-electron computations of the profiles in the parent compound La 2CuO4 within the local density approximation (LDA) based conventional band- theory framework, assuming that the resulting metallic state is representat ive of the Sr-doped compound. Although the experimental anisotropy of the p rofiles, DeltaJ = J([001]) - J([100]), and the first and second derivatives of the profiles are in reasonable overall accord with the computations, th ere are striking discrepancies as well. We suggest that these discrepancies may indicate a substantially larger O 2p character of the doped holes in L a2CuO4 than implicit in the standard band-theory picture. (C) 2001 Elsevier Science Ltd, All rights reserved.