Reports are flying around the Web that speak of the creation of a fabled quantum material that may have some relatively magical properties. Whenever anyone suggests that a new quantum material has been discovered, skepticism should be front and center.
Indeed, in this case, the material hasn’t actually been manufactured, despite the fact that a new theoretical physics model has pointed toward it existing. So what exactly is it?
Writing in the Proceedings of the National Academy of Sciences, the team – led by Rice University – explain that it’s a “Weyl-Kondo semimetal” that shares its properties with a wide range of other materials that exhibit curious quantum behavior. This includes a strange class of materials known as “topological insulators”, a topic that featured in 2016’s Nobel Prize in Physics.
Quantum materials exhibit unusual properties and electromagnetic behavior that cannot be exclusively explained using classical physics, which attempts to explain gravity, electromagnetism, and nuclear forces without invoking quantum mechanics.
Take superconductors, for example. These materials, when cooled to temperatures near to absolute zero, experience a dramatic drop in electrical resistance. This means that a current can propagate around the superconducting material without the material heating up (potentially dangerously), which is clearly an extremely useful property to have in some instances.
This phenomenon is quantum mechanical in nature, which means that it’s already strange. However, things get weirder.
In the 1980s, certain superconducting materials were discovered to still be able to carry currents at zero resistance at bizarrely high temperatures. This makes them far more efficient than regular old superconducting materials.
These high-temperature superconductors are also quantum materials that can’t be explained using classical physics, and right now, according to a recent editorial in Nature, “the mechanism of superconductivity continues to be elusive.”
There’s much we don’t know, even when we come across a brand new quantum material.
That’s the case with this new Weyl-Kondo semimetal. While experimenting with a range of models that were designed to help explain things like high-temperature superconductivity, they serendipitously happened across what seemed like evidence for a Weyl fermion.
Fermions follow a certain set of rules in quantum mechanics. They include quarks, electrons, protons, and others. Weyl fermions, which remain hypothetical, are odd in that they appear to be lacking in any mass whatsoever, and that is what the team’s models appear to have conjured up.
"The massless property of Weyl fermions comes from the fact that their energy doesn't depend on mass, which means they bear a resemblance to photons," co-author Sarah Grefe, a graduate student of physics at Rice University, told IFLScience. Essentially, these fermions still have mass, but "they just effectively act like they don't have one."
Now, Weyl fermions are thought to exist in certain materials that conduct electrical currents. Materials known as topological conductors, for example, are suspected of carrying electricity through their interior, thanks to the presence of these Weyl fermions.
The first solid evidence of their existence dates back to 2015, when three independent groups of physicists spotted them for the first time in a semimetal named tantalum arsenide. This was based on somewhat indirect evidence of a “formation” known as a Fermi arc.
What the team headed by Rice University has now found is additional model evidence for a new type of quantum material featuring these Weyl fermions. But wait – what’s with the “Kondo” part?
The so-called Kondo effect explains that electrons within a magnetic metal are sometimes scattered due to a chemical impurity. This ends up altering the material’s ability to resist electrical current, depending on what its temperature is.
It appears that, according to the team’s models, the Kondo effect is the progenitor of the Weyl fermions they observed. Thus, the quantum material their work points to has been dubbed a “Weyl-Kondo semimetal”.
Again, this material does not yet exist. With this work, however, it soon might – and who knows what bonkers properties it’ll have when it does emerge?