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.
@article{arxiv.cond-mat/0502357,
title = {Spectroscopy of stripe order in La1.8Sr0.2NiO4 using resonant soft x-ray diffraction},
author = {C. Schuessler-Langeheine and J. Schlappa and A. Tanaka and Z. Hu and C. F. Chang and E. Schierle and M. Benomar and H. Ott and E. Weschke and G. Kaindl and O. Friedt and G. A. Sawatzky and H. -J. Lin and C. T. Chen and M. Braden and L. H. Tjeng},
journal= {arXiv preprint arXiv:cond-mat/0502357},
year = {2009}
}