Speak of the Demon

Discovery of strange behavior of new plasmons predicted in the 50s
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Kyoto, Japan -- In 1956, the US theoretical physicist David Pines predicted a strange state of electrons in solids. Normally, electrons have a mass and an electric charge, but Pines asserted that electrons can combine to form composite particles that are massless, electrically neutral, and do not interact with light. These particles called DEM-ons -- or particles of distinct electron motion -- have never actually been observed.

Now, 67 years after the Pines’ Demon was predicted, it was successfully observed by Peter Abbamonte’s group at the University of Illinois at Urbana-Champaign, USA, in collaboration with Yoshiteru Maeno at the Toyota Riken - Kyoto University Research Center. Using a special technique that directly excites the electronic mode of matter, they observed the demon behavior in strontium-ruthenium oxide.

"We investigated the properties of fascinating quantum matter with a new technique and observed a novel signal. At first, the mechanism was not understood and the submitted paper was not accepted. Recently, from the viewpoint that we may have observed the "demon" predicted by Dr. Pines, we also carried out a detailed theoretical analysis and were able to explain the actual data, which led to the publication of the paper. In the future, we will investigate the detailed behavior of the demons in this material and hope to expand our research to other materials with similar properties," says Yoshiteru Maeno, formerly of KyotoU's Graduate School of Science.

Caption: Oscillatory electron densities for (top) ordinary plasmons and (bottom) Pines' demons. Electrons in the β (beta) and γ (gamma) bands are depicted in red and blue.
Credit: KyotoU/Yoshiteru Maeno
Yoshiteru Maeno
Publication information



Ali A. Husain, Edwin W. Huang, Matteo Mitrano, Melinda S. Rak, Samantha I. Rubeck, Xuefei Guo, Hongbin Yang, Chanchal Sow, Yoshiteru Maeno, Bruno Uchoa, Tai C. Chiang, Philip E. Batson, Philip W. Phillips, Peter Abbamonte (2023). Pines' demon observed as a 3D acoustic plasmon in Sr₂RuO₄. Nature, 621(7977), 66-70.