Spin-Orbit Excitons in a Correlated Metal

April 02, 2024


Multi-band metals are currently of major interest in the quantum materials community, as epitomized by unconventional superconductors such as FeSe and Sr2RuO4. Since the valence electrons are spread out over several energy bands and Fermi surfaces, capturing their mutual interactions and their influence on the macroscopic phase behavior is a major theoretical challenge. We have carried out a combined Raman scattering and theoretical study of spin-orbit excitations in the disorder-free multi-band metal Sr2RhO4, where prior experiments had revealed sharp Fermi surfaces. We observe unusual but well-defined excitations around 230 meV, and identify them as excitonic transitions between the spin-orbit multiplets of the Rh ions, analogous to those recently observed in the Mott insulators Sr2IrO4 and RuCl3. Our discovery of atomic-like electronic excitations in a clean d-electron metal opens up a rich source of information on electronic correlations in multi-band metals.

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