Condensed matter physicists from the University of Illinois have successfully summoned a demon, but probably not the one you’re picturing—think less fire and brimstone and more quantum mechanics trickery. The “demon,” in this case, actually stands for “distinct electron motion” with the physics favorite suffix “-on” added for good measure.
Theorized by physicist David Pines in 1956, this demon (also known as Pine’s Demon) is a plasmon—a discrete wave rippling through plasma electrons—that is massless and has a neutral charge. As you’d probably imagine, something that’s both massless and neutral isn’t exactly easy to detect.
But a new paper published by scientists at the University of Illinois showcases how they stumbled upon this demon plasmon by accident. At first, the team was only analyzing the metal strontium ruthenate to figure out why it contained similar properties to high-temperature superconductors (around -130 degrees Celsius) without actually being one. Then, they spotted a quasiparticle that was too slow to be a surface plasmon but too fast to be an acoustic phonon.
“At first, we had no idea what it was. Demons are not in the mainstream. The possibility came up early on, and we basically laughed it off,” co-author Ali Husain said in a press statement. “But, as we started ruling things out, we started to suspect that we had really found the demon.”
To find the demon, the team fired electrons off a crystal of the metal strontium ruthenate and measured energy gain with an incredibly high precision. Using this energy data, scientists could then track the demon’s momentum within the material until finally discovering that the quasiparticle closely matched Pine’s 67-year-old predictions of a massless electronic mode, or demon. The results were published this week in the journal Nature.
“It speaks to the importance of just measuring stuff,” Peter Abbamonte, physics professor at the University of Illinois Urbana-Champlain and co-author, said in a press statement. “Most big discoveries are not planned. You go look somewhere new and see what’s there.”
The discovery of a demon is particularly important for understanding superconductors. Because this quasiparticle is massless, it can form with any energy and potentially at any temperature.
The standard theory of superconductors, known as the BCS theory, attributes superconductivity to an interaction between electrons and phonons, the natural vibrations given off by an atomic crystal lattice. However, the BCS Theory can’t always explain the zero energy resistance of high-temperature superconductors, which suggests some materials achieve superconductivity through other means. One of these means could be this newly discovered demon quasiparticle, as they’ve been theorized to play a role in a semimetal’s transition into superconductivity.
The first step in any breakthrough is to first face your demons—hopefully, the same can be said for superconductors as well.
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