Towards a limited XANES refinement in strongly correlated systems

Three components of O1 atom displacements have been derived from the direct fit of the polarized Ellab Cu K-edge XANES spectrum of Nd(1.85)Ce(0.15)CUO(4-delta) superconductor. The best fit is achieved for a 60 to 40% mixture of 2x2 undistorted antiferromagnetic and modified charge density wave (MCDW) domains. The local structure of the MSDW is characterized by correlated displacements of deltaO1 parallel = 0.12 +/- 0.04, deltaO1 perpendicular = 0.25 +/- 0.08, and deltaO1z = 0.12 +/- 0.1 A. An agreement factor over the range of 8980-9040 eV is 2-3 times smaller than it may be obtained from single-electron MS calculations. This improvement comes from accounting for many-body excitations and the relationship between electronic and local structure in the CuO2 planes.