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Resonant Inelastic X-ray Scattering from 4D Metals: First Results from the IRIXS Project

Resonant Inelastic X-Ray Scattering (RIXS) has firmly placed itself as an important experimental technique to study magnetic, charge, and orbital excitations in strongly correlated systems. The most studied classes of materials are the superconducting cuprates (using RIXS at the Cu L3-edge ~930 eV) and the strongly spin-orbit coupled iridates (using RIXS at the Ir L3-edge ~11.215 keV). These two families represent systems studied with soft- and hard-x-rays, respectively, covering the 3d and the 5d transition metal oxides (TMO). Although there is a handful of beamlines for each of those x-ray energy ranges (soft and hard), none exists today that can bridge the gap between them (intermediate). Here I will present an ongoing project at Petra III DESY where a collaboration between the Max-Planck Institute in Stuttgart (Prof. Keimer) and beamline P01 has been established, resulting in the first intermediate x-ray energy RIXS spectrometer (IRIXS). The IRIXS instrument has been designed to cover the L3 and L2 edges of Ru (2.840 and 2.970 keV), representing a huge scientific opportunity to look at the intriguing ruthenates (e.g. p-wave superconductivity in Sr2RuO4 and Kitaev physics in alpha-RuCl3). I will cover the experimental challenges introduced by the use of intermediate x-rays as well as present evidence for excitonic magnetism in Ca2RuO4 and the first RIXS observation of a single magnon in a Ru-based system. These results are quite encouraging and pave the way for a state of the art Ru L3/L2-edge RIXS spectrometer, where resolution comparable to the Cu and Ir L3-edge RIXS will be pursued.