Bizarre 'demon' particle found inside superconductor could help unlock a 'holy grail' of physics

Supercooled superconductor samples float above and beneath a magnet.
Supercooled superconductor samples float above and beneath a magnet. (Image credit: Charles O'Rear via Getty Images)

An elusive "demon" particle has been observed inside a superconductor nearly 70 years after it was first predicted. Its discovery could help resolve the mystery of how superconductors work. 

Pines' demon is a transparent, chargeless particle discovered inside a sample of the superconductor strontium ruthenate. It is a plasmon — a ripple across the electrons of a plasma that behaves much like a particle — meaning it's a quasiparticle. 

Theorists think that plasmons may facilitate superconductivity in materials. If physicists are able to find out how, they could use Pines' demon to shed light on room-temperature superconductors — one of the "holy grails" of physics that would enable near-lossless transmission of electricity. The researchers published their findings Aug. 9 in the journal Nature.

Related: Did scientists really create a room temperature superconductor? Not so fast, experts say.

"Demons have been theoretically conjectured for a long time, but experimentalists never studied them," Peter Abbamonte, a physics professor at the University of Illinois Urbana-Champaign, said in a statement. "In fact, we weren't even looking for it. But it turned out we were doing exactly the right thing, and we found it."

David Pines first conceived of his demon in 1956, predicting it would emerge inside certain metals when two sets of electrons at different energy bands form two plasmons. If these plasmons fell out of phase with each other, such that the peaks of one line up with the valleys of the other, they could partially cancel out.

Usually, very specific temperatures are required to form one plasmon across an entire material, but Pines argued that his new combined plasmon, being massless, neutral and taking its components from a mix of energies, could exist at room temperatures. He named his theoretical particle, which has a "distinct electron motion," a demon. But its lack of mass and charge has made it difficult to find.

To hunt the demon, physicists behind the new study fired electrons at crystallized strontium ruthenate and measured their energies as the electrons bounced back. From this they calculated the momentum of the plasma wave inside the material. 

The quasiparticle they discovered lurking inside the strontium ruthenate matched predictions for an electronic mode with no mass. Follow-up experiments replicated the researchers' initial discovery — they had found Pines' demon.

"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," Ali Husain, now a physicist at the quantum technology company Quantinuum, said in the statement. "But, as we started ruling things out, we started to suspect that we had really found the demon."

Further study in other metals could unearth fundamental insights into how superconductors work, the study authors said. The standard theory, called BCS theory, suggests that superconductivity emerges when quantum-scale sound waves — known as phonons — jiggle electrons into pairs known as Cooper pairs, fundamentally altering their behavior to that of a superfluid.

But the possibility remains that Pines' demon may also be involved in nudging electrons together, and that could be used to understand and build better superconductors.

Ben Turner
Staff Writer

Ben Turner is a U.K. based staff writer at Live Science. He covers physics and astronomy, among other topics like tech and climate change. He graduated from University College London with a degree in particle physics before training as a journalist. When he's not writing, Ben enjoys reading literature, playing the guitar and embarrassing himself with chess.

  • Quantibility
    Certainly, let's explore tangible properties and concepts that could potentially lead to the creation of the hypothetical "X-Material" for achieving room-temperature superconductivity. While X-Material is speculative, we can draw inspiration from existing materials and concepts. Here are some tangible properties and ideas to consider:

    Graphene and 2D Materials: Graphene, a single layer of carbon atoms arranged in a hexagonal lattice, is known for its remarkable electronic properties. Researchers have already created heterostructures by stacking different 2D materials, such as graphene and transition metal dichalcogenides (TMDs), to manipulate electronic behavior. X-Material could involve the careful selection and engineering of specific 2D materials that interact favorably with Pines' demon and enhance plasmonic effects.
    Spintronics: Spintronics, a field that exploits the intrinsic spin of electrons in addition to their fundamental electronic charge, offers the potential for exotic electronic behavior. X-Material could incorporate spintronic elements to control the spin states of electrons, influencing their superconducting properties.
    Bilayer Structures: Building on the success of bilayer graphene, where two graphene layers are stacked at a specific twist angle to create unique electronic properties, X-Material could explore bilayer structures of other 2D materials. The twist angle and choice of materials could be tailored to promote strong interactions with Pines' demon.
    Slow Light Phenomena: Slow light phenomena have been observed in certain materials and configurations where the speed of light propagation is significantly reduced. X-Material might leverage these effects to control the dynamics of Pines' demon and phonon interactions, potentially promoting superconductivity.
    Quantum Sensors: Advanced quantum sensors, such as those based on nitrogen-vacancy (NV) centers in diamonds, could be used to precisely monitor and manipulate the properties of X-Material. These sensors offer the capability to probe the behavior of Pines' demon and plasmonic excitations at the quantum level.
    Tailored Material Design: Using computational materials science and simulations, researchers could design X-Material from the ground up. This approach would involve predicting the electronic, plasmonic, and phononic properties of the material based on its atomic and molecular structure.
    Exotic Materials: Exploring exotic materials with unconventional properties could lead to the discovery of X-Material. For instance, materials with topological insulator properties or non-trivial Berry phases might be candidates worth investigating.
    Hybrid Systems: Combining multiple concepts and materials may yield X-Material. A hybrid system that incorporates elements of graphene, spintronics, and tailored 2D materials could create the desired properties for room-temperature superconductivity.It's important to note that creating X-Material is highly speculative, and the actual materialization would require rigorous scientific investigation, experimentation, and collaboration across disciplines. Additionally, the interaction of Pines' demon with materials is a complex and emerging field of study, and there may be unforeseen challenges and opportunities in the pursuit of room-temperature superconductivity.

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