Physicists Confirm Prediction of Massless Neutral Particle

Physicists Confirm Prediction of Massless Neutral Particle
Physicists Confirm Prediction of Massless Neutral Particle - High-energy M-EELS spectra from Sr2RuO4. a, Conceptual illustration of the reflection M-EELS experiments from a split Sr2RuO4 surface. b, Constant-q (in rlu) energy loss scans for a selection of q values ​​along the (300) crystallographic direction taken at T = 1,0 K. These spectra were obtained by dividing and scaling the M-EELS matrix elements. curves as described in ref. 37. At small moments (q < 0.16 rlu), the spectra show a broad plasmon characteristic peaking at 1.2 eV. At larger momenta, the data show an energy-independent continuum, as previously observed in Bi2Sr2CaCu2O8+x (ref. 37). Nature: (2023). DOI: 10.1038/s41586-023-06318-8

David Pines, a theoretical physicist, suggested in 1956 that electrons in a material could behave strangely. Pines claimed that electrons could combine to form a composite particle that is massless, neutral, and typically has a mass and an electric charge, but does not interact with light. He referred to this particle as "the devil". Since then, it has been assumed to have a significant influence on how various metals behave. Since predicted, it has unfortunately managed to avoid detection due to the same features that make it interesting.

67 years after the existence of the demon of Pines was predicted, a research team led by Peter Abbamonte, professor of physics at the University of Illinois at Urbana-Champaign, has now discovered the monster. According to the news published in the journal Nature, the researchers stated that the devil's signature can be seen in the metal strontium ruthenate, thanks to an unusual experimental method that directly activates the electronic states of a material.

According to Abbamonte, there have been theories about demons for a long time, but experimenters never investigated them. In fact, we didn't even research it. However, it turned out that we did everything right, and we discovered it.

The loss of their unique properties in solids is one of the most important discoveries in condensed matter physics. Electrons combine to form collective units as a result of electrical interactions. Electrons, if they have enough energy, can even combine to produce compound particles known as plasmons with new charges and masses defined by the underlying electrical interactions. However, the mass is typically so large that plasmons cannot form at ambient temperature using available energies.

Pines discovered an anomaly. He suggested that if a solid contained electrons in more than one energy band, as many metals do, then the plasmons of each band could combine in an out-of-phase order to form a new, massless, neutral plasmon called the devil.

Since demons have no mass, they can be created with any energy, allowing them to exist at any temperature. This has led to the theory that multiband metals significantly influence their behavior.

Demons are neutral, so normal condensed matter experiments won't detect their presence. According to Abbamonte, demons are electrically neutral, so they do not interact with light. “The vast majority of experiments are done with light and measure optical properties,” he said. “We needed a completely different kind of experiment.”

Abbamonte remembers that he and his colleagues were doing research on strontium ruthenate for another reason—the metal looks like high-temperature superconductors without actually being superconducting. They were conducting the first study of the metal's electrical properties to reveal clues as to why the event occurred in other systems.

Abbamonte and former graduate student Ali Husain used momentum-resolving electron energy loss spectroscopy to analyze high-quality samples of the metal synthesized by Yoshi Maeno's research team at Kyoto University. This is an unusual method that uses the energy of electrons fired into the metal to observe the metal's properties, particularly the resulting plasmons. But while examining the data, the researchers discovered something strange: an electric mode devoid of mass.

Husain recalls: “At first we had no idea what was going on. I am now a research scientist at Quantinuum. Demons are generally not accepted. At first, this possibility came up, and we laughed it off. However, as we began to rule out possibilities, we began to wonder if we had really located the devil.

Condensed matter theorist Edwin Huang, a Moore Postdoctoral Fellow at UIUC, was eventually tasked with calculating the properties of the electronic structure of strontium ruthenate. “Pines' demon prediction requires quite specific conditions, and it wasn't clear to anyone whether strontium ruthenate should have a demon,” he said. “We had to do a microscopic calculation to figure out what was going on.

When we did this, we discovered a particle consisting of two bands of electrons oscillating out of phase with approximately equal amplitude, just as Pines predicted.

Abbamonte said it was no coincidence that his team discovered the demon "by chance". Abbamonte stressed that he and his team are working with a drug that hasn't been studied in depth before, and a procedure that isn't widely used. They think they discovered something unexpected and important just by trying something different.

He added that this highlights the value of simply taking measurements. “Most important discoveries are unpredictable. You explore a new area to see what's available.


📩 12/08/2023 12:45