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Identification of orbital state of excited electron by polarization-analyzed inelastic x-ray scattering

Jun. 14, 2011

A joint research group has established a technique to identify the orbital state of the excited electron in inelastic x-ray scattering using synchrotron radiation x-rays at SPring-8. The group consists of Japan Atomic Energy Agency (JAEA), Tohoku University, High energy accelerator research organization (KEK), and International Institute of Advanced Studies (IIAS).

Orbital state determines the shape of electronic wave function in an atom. In transition metal compounds, such as high-Tc superconducting copper oxides, the orbital state of the d electron plays an important role in the physical properties of the compounds. For example, it controls the anisotropy of mobility of the electrons and propagation of interactions. Resonant inelastic x-ray scattering (RIXS) is one of the experimental methods to measure orbital excitations, where the orbital state changes by gaining energy of x-ray. However various excitations are entangled in the spectrum of RIXS and it has been difficult to distinguish them experimentally so far.

The research group utilized the polarization, which in an inherent and important characteristic of the photon, and developed a polarization analyzer of the scattered x-rays in RIXS. Using this analyzer, it was demonstrated in the transition metal compound KCuF3 that one can distinguish the excited orbital states by polarization-analyzed RIXS technique.

This new technique enables us to identify the electronic excitations which are closely related to the physical properties in transition metal compounds independently of the parameters in theoretical models, because symmetry of the orbital states is rigorously connected to the polarization of the photon. It would facilitate the understanding of attractive physical properties and functions in the transition metal compounds.

The research results were partly supported by Core Research for Evolutional Science and Technology (CREST) of Japan Science and Technology Agency (JST) and have been published in rapid communications “Physical Review BE(a scientific journal issued by American Physical Society) as EditorsEsuggestion on June 16, 2011.

Orbital states of d electron in transition metal compounds. Energy of the electron depends on the orbital states. One can observe the change of the orbital state accompanied with energy transfer from x-ray to the electron in inelastic x-ray scattering.

Polarization-analyzed resonant inelastic x-ray scattering spectra of KCuF3. The orbital excitations are observed at 1.0-1.5 eV. The polarization of the scattered x-rays is perpendicular and parallel to the scattering plane in the red and blue spectra, respectively. Only the lower orbital excitation (red arrow) is observed in the former polarization condition while both upper and lower excitations (blue arrows) are observed in the latter.

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