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Resonant inelastic x-ray scattering (RIXS)

experiments: Mark Dean
theory: Yilin Wang 

RIXS is a technique in which one measures the change in energy and momentum of X-rays that scatter from a material as illustrated in the figure below. This technique has great potential for probing the low energy excitations in correlated electron materials, as it can be used to study charge, magnetic, lattice and orbital excitations [Rev. Mod. Phys. 83, 705-767 (2011)]. Furthermore, it is element and orbital resolved, bulk sensitive and compatible with small samples. With the advent of x-ray free electron lasers it can even be applied to ultra-fast transient states [Nat. Mat. 15, 601-605 (2016)]. 

photo of spectrometer

Example of the RIXS process from J. Magn. Magn. Matt. 376, 3–13 (2015). The initial |i>, intermediate |n>, and final |f >, states appear from left to right. Red spheres represent states filled by electrons and black spheres denote holes with up or down spin. Wavy yellow lines illustrate incoming and outgoing photons. The blue arrows depict transitions. In this process spin excitations are created with energy, ℏωk-ℏωk’ and momentum ℏq = ℏk-ℏk’.

Despite the usefulness of RIXS, the three state scattering process that includes a core hole makes it challenging to interpret or calculate theoretically. Theorists Yilin Wang and Gabi Kotliar and experimentalists Mark Dean, Derek Meyers and Gilberto Fabbris have been working on methods to theoretically calculate and experimentally verify RIXS using the soft inelastic x-ray (SIX) beamline at the National Synchrotron Light Source II (NSLS-II) that is currently being commissioned. An open source toolkit EDRIXS (see it on GitHub) has been developed to simulate RIXS spectra. Recent successes include a study aimed to identify dimer orbitals in an iridate material Ba5AlIr2O11 [Phys. Rev. Lett. 122, 106401 (2019)] and a study aimed to clarify the nature of the “hidden order” in URu2Si2 [Phys. Rev. B 96, 085146 (2017)].

Related Publications

Resonant inelastic x-ray scattering studies of elementary excitations.
Luuk J. P. Ament, Michel van Veenendaal, Thomas P. Devereaux, John P. Hill, and Jeroen van den Brink,
Rev. Mod. Phys. 83, 705 (2011)

Insights into the high temperature superconducting cuprates from resonant inelastic X-ray scattering.
J. Magn. Magn. Matt. 376, 3–13 (2015)

Ultrafast energy- and momentum-resolved dynamics of magnetic correlations in the photo-doped Mott insulator Sr2IrO4.
M.P.M. Dean, Y. Cao, and J. P. Hill,
Nat. Mat. 15, 601-605 (2016)

On the possibility to detect multipolar order in URu2Si2 by the electric quadrupolar transition of resonant elastic x-ray scattering.
Y. L. Wang, G. Fabbris, D. Meyers, N. H. Sung, R. E. Baumbach, E. D. Bauer, P. J. Ryan, J.-W. Kim, X. Liu, M. P. M. Dean, G. Kotliar, and X. Dai,
Phys. Rev. B 96, 085146 (2017)

Direct Detection of Dimer Orbitals in Ba5AlIr2O11
Y. Wang, Ruitang Wang, Jungho Kim, M.H. Upton, D. Casa, T. Gog, G. Cao, G. Kotliar, M.P.M. Dean and X. Liu
Phys. Rev. Lett. 122, 106401 (2019)

EDRIXS: An open source toolkit for simulating spectra of resonant inelastic x-ray scattering
Y. Wang, G. Fabbris, M.P.M. Dean and G. Kotliar
Computer Physics Communications 243, 151-165 (2019)