Spectroscopy of stripe order in La1.8Sr0.2NiO4 using resonant soft x-ray   diffraction
  Strong resonant enhancements of the charge-order and spin-order superstructure-diffraction intensities in La1.8Sr0.2NiO4 are observed when x-ray energies in the vicinity of the Ni L2,3 absorption edges are used. The pronounced photon-energy and polarization dependences of these diffraction intensities allow for a critical determination of the local symmetry of the ordered spin and charge carriers. We found that not only the antiferromagnetic order but also the charge-order superstructure resides within the NiO2 layers; the holes are mainly located on in-plane oxygens surrounding a Ni2+ site with the spins coupled antiparallel in close analogy to Zhang-Rice singlets in the cuprates. 
C. Schuessler-Langeheine, J. Schlappa, A. Tanaka, Z. Hu, C. F. Chang,   E. Schierle, M. Benomar, H. Ott, E. Weschke, G. Kain...