Observation of Spin Fluctuations in a High-Tc Parent Compound Using   Resonant Inelastic X-ray Scattering
  We report the first observation of soft-x-ray scattering from spin fluctuations in a high-Tc parent compound. An antiferromagnetic charge transfer insulator, CaCuO2, was irradiated by Cu M-edge soft x-rays. Ultra-high resolution measurements of scattered intensity revealed magnon-magnon excitations, due to spin exchange scattering, as low-energy loss features. The process is analogous to optical Raman scattering. The spectra provide the first measurement of the two-magnon excitation energy and the antiferromagnetic exchange parameter in infinite-layer CaCuO2. The results reveal resonant inelastic soft x-ray scattering as a novel probe of the spin dynamics in cuprates. 
B. Freelon, P. G. Medaglia, A. Tebano, G. Balestrino, K. Okada, A.   Kotani, F. Vernay, T. P. Devereaux, P. A. Glans, T. Lea...