Physicists researching an exotic material discovered a significant quantum event predicted decades ago.
Pines’ Demon, predicted by late physicist David Pines in 1956, has been discovered in a substance named strontium ruthenate (Sr2RuO4) for the first time in an equilibrium 3D metal.
Pines’ Demon is projected to play a major role in a variety of phenomena, including transitions in specific types of semimetals and superconductivity, hence the research has important implications for material physics.
“We found this thing by accident,” said University of Illinois physicist Peter Abbamonte during a discussion about the discovery.
“We saw this excitation back in 2018, and it took us a while to figure out what it was, and it turned out to be this demon mode.”
It’s actually a sort of plasmon, which is a discrete wave unit that moves through an electron population. It has been said that plasmons are the quantum equivalent of an acoustic sound in a classical gas.
Because this plasmon represents a unique electron motion, or D.E.M., Pines gave it the name “demon” in honor of James Clerk Maxwell, who created Maxwell’s devil.
A sound wave that is moving through a group of particles gradually becomes quieter when the jiggling stops. A plasmon is very all-or-nothing, contrary to how quantum mechanics “sounds,” though. Every increase in frequency requires a very specific quantity of energy.
A plasmon frequency without an associated electrical charge is Pines’ devil. They happen when the energy bands or ranges of electrons in a material shift out of phase.
There is a change in the occupancy of the bands but no energy transfer. A neutral collective mode that has been screened or damped by another band of electrons is referred to as a “demon”.
Plasmons have been observed and extensively investigated in 2D metals, but they are challenging to find since they are electrically neutral and don’t couple with light. Now let’s talk about strontium ruthenate.
The substance performs as a superconductor at low temperatures. It becomes a little strange at higher temperatures and transforms into a “bad metal,” a substance whose properties don’t always behave as we would expect them to.
It’s also a great candidate for the identification of demons, according to a team led by physicist Ali Husain, formerly of the University of Illinois in the US and now at the University of British Columbia in Canada. It has three nested bands of electrons, two of which contrast similarly to the original 1956 conceptualization of the demon.
When Husain was using electron spectroscopy to analyze strontium ruthenate, he noticed something in the data that appeared to be a quasiparticle, or a collective excitation that behaved like a particle.
Numerous known quasiparticles exist, however the researchers’ discovery did not correspond to any of them. Its velocity was both too rapid and too sluggish to be an acoustic phonon or a surface plasmon.
The most likely possibility, according to further investigation, was a demon, and the team even managed to duplicate the finding. Additionally, a review of certain of its characteristics led to some doubts.
For instance, the damping effect was less pronounced than predicted, and there were odd holes in the various electron bands.
That’s pretty much where the science stands right now, but it’s certainly ready for more investigation—especially given the possibility that demons have an important role to play in superconductivity.
The scientists think that higher-resolution investigations using scanning electron microscopy may be feasible, and that other multi-band metals may be appropriate places to examine them in order to see how their behavior can change in a variety of circumstances.
They are hoping that this will help them find the answers to their new inquiries and develop a more thorough and comprehensive theory of demons.
The research has been published in Nature.
