Orbital physics (Communication arising)

Experimental quest for orbital waves

Abstract

One challenge in condensed-matter physics is the experimental confirmation of a new kind of elementary excitation — orbital waves, or orbitons, which are predicted to exist in an orbitally ordered state. Saitoh et al.1 have observed three peaks at 160, 144 and 126 meV in the Raman scattering of orbitally ordered lanthanum manganate (LaMnO3), and interpret these as evidence of orbitons. However, we find similar peaks in the optical conductivity, σ(ω), of LaMnO3 and point out that the direct observation of orbitons in σ(ω) is prohibited by a selection rule. This suggests that the Raman peaks observed by Saitoh et al. arise from multiphonons, and that the existence of orbitons has yet to be experimentally confirmed.

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Figure 1: Optical conductivity σ(ω) of LaMnO3 and LaCoO3, and Raman measurements on LaMnO3 at a temperature of 4 K.

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Correspondence to M. Grüninger.

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Grüninger, M., Rückamp, R., Windt, M. et al. Experimental quest for orbital waves. Nature 418, 39–40 (2002). https://doi.org/10.1038/418039a

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