The study of magnetic excitations of cuprates with Resonant Inelastic X-Ray Scattering: results and perspectives

Lucio Braichovich, Politecnico Milano

Abstract
We have found (Phys. Rev. Lett. 102,167401 (2009), 103, 117003 (2009) and 104, 077002 (2010)) that Resonant Inelastic X-ray Scattering (RIXS) at the L3-edge of Copper can be used to measure the dispersion of spin excitations in cuprates, undoped and doped. Up to now this was possible only with neutron scattering. Indeed the x-rays (used in the RIXS mode) extend dramatically the possibilities of experimental work since it becomes possible to study very tiny objects not accessible to neutrons as thin films and, in perspective, nano-objects having both fundamental and technological interest. The cases of La2CuO4 and L(2-x)SrxCO will be used as a benchmark and in particular we will show that single magnons are seen with RIXS in La2CuO4 in perfect agreement with neutrons. Moreover the x-rays have already shown new features in doped systems not seen with neutrons so that the cross fertilization between the two approaches is expected to be particularly promising. In particular in L(2-x)SrxCO we have seen spin excitations up to high energies (around 300 meV) surviving to doping in the under-doped regime (8% holes) a fact not known up to now. We show also that the sensitivity and selectivity of RIXS allows the study of the strain effects on very thin films of CaCuO2; this new approach gives the simultaneous measurement of the 'pressure' effect on super-exchange and on crystal field. Moreover also results on Nd123 will be presented. Finally the RIXS perspectives will be discussed.

X-ray microscopy: nanoscale imaging of materials in their complexity

Chris Jacobsen, Northwestern University

Abstract
X-ray microscopes at many facilities worldwide are able to deliver 30-60 nm resolution images as a matter of routine, and efforts pushing towards 10 nm or below are under active pursuit. However, spatial resolution should not be the primary goal, since electron microscopy at 0.2 nm resolution has been in place for decades. Instead, x-ray microscopy offers important new capabilities for imaging materials that are thick, wet, and (in some cases) functional; with spectroscopic information on trace elements and electronic state configuration; and in 3D. Following an overview of lens-based and lensless microscopy activities, challenges for future x-ray microscopy will be described, including computational methods for dealing with the complexity of spectroscopic image data, and cryo methods for dealing with the effects of radiation damage.