Scientists Found Dark Electrons: a Secret Quantum State Hidden in Solid Matter
A Secret Quantum State Hidden in Solid Matter
- Researchers have just found evidence of “dark electrons”—electrons you can’t see using spectroscopy—in solid materials.
- By analyzing the electrons in palladium diselenide, the team was able to find states that functionally cancel each other out, blocking the electrons in those “dark states” from view.
- The scientists believe this behavior is likely to be found across many other substances as well, and could help explain why some superconductors behave in unexpected ways.
If you were to shine a flashlight onto a blank wall, you may be surprised to see that the beam makes a series of rings wherever it lands. That’s a result of what’s called interference—the waves of light crashing into each other more or less in sync. If the waves are synched up, you have constructive interference, and you get a brighter signal. If the waves don’t line up, you have destructive interference, and you get a darker signal. If the waves are perfectly ‘opposite,’ the destructive interference is at its most extreme, and you get no signal at all.
Light is the easiest example, but it’s not the only thing that experiences interference. Interestingly, electrons can interfere as well if they have perfectly different energies. This can lead to the existence of ‘dark electrons’—electrons in ‘dark states’ that are you can’t see with a spectroscope.
For a long time, we thought these secretive electrons simply didn’t exist in solid materials. The electrons can’t get all that far removed from each other, so those ‘perfectly different energies’ were thought not to be possible. But recently, a group of scientists lead by researchers from South Korea found that these states occur even in condensed matter, which could have a significant effect on our understanding of quantum physics. A paper on these findings was recently published in the journal Nature Physics.
“This hidden state could be a missing piece of information that is critical to understand quantum phenomena that have remained elusive,” the authors wrote in the paper. “It is, therefore, fundamentally important to identify the existence of other hitherto unknown dark states in nature and to disclose their underlying mechanisms.”
The researchers first went digging for these dark states in a crystalline material called palladium diselenide, or PdSe2. Taking a look at the behavior of electrons in this material, the team found entire bands that they knew were meant to be present, but that they simply couldn’t see. They examined the material using several polarizations of light in order to make sure that the dark states they were seeing were the result of the electrons themselves and not the light being used to examine them.
Once they found their bands, the researchers used models to extrapolate their finding into other systems. And excitingly, they were able to generalize their results fairly easily (well, as easily as you can do anything in quantum mechanics). Their findings imply that the dark electrons they found in PdSe2 aren’t just a fluke—they’re a sign that dark states are likely found all throughout nature.
As Keun Su Kim—one of the authors on the study—told New Scientist, this discovery has the potential to explain why some surprising materials behave like superconductors under unexpected conditions. If we can’t even see part of their quantum behavior, it’s no surprise we couldn’t make heads or tails of it before. But knowing what we’re looking for could now lead to some much-needed explanations.
Darkness in science often means mystery. But mysteries can be answers in and of themselves—at least, until you dig even deeper.
