This manuscript presents the discovery of a quasiparticle called “demon” (from “distinct electron motion” or d.e.m.) that was predicted 66 years ago by David Pines and not observed definitively until now. The characteristic excitation of a metal is a plasmon, which is a quantized excitation of its electron density, and is commonly observed in elemental metals as well as in a number of quantum materials. In 1956, David Pines predicted that a distinct type of plasmon—a demon—could exist in multiband metals with more than one species of charge carrier. However, there has been no definitive evidence that demons actually exist. By using momentum‐resolved electron energy‐loss (M‐EELS) spectroscopy, we observe a gapless and charge-neutral demon excitation in the multiband metal Sr2RuO4. Check out the original paper here!
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