When things don’t make sense in the quantum realm, scientists don’t always get to find a good explanation for what they’re seeing. Many times, they arrive at a solution by accident—something that usually begins with the realization that a weird signal is not a wrong signal.
Researchers had known about an odd phenomenon in which an initially conductive material seemingly loses its ability to conduct electricity altogether. Although physicists suspected electrons were involved, they struggled to pinpoint the exact mechanism. But a new paper published in Physical Review Letters identifies the culprit—or, rather, culprits—behind this disappearing act: an amalgamation of particles referred to as polarons.
This specific arrangement creates a strange “dance” between the electrons and surrounding atoms that eventually blocks the flow of electricity in the material, according to the researchers. The findings represent the first time polarons were found inside a compound based on thulium, selenium, and tellurium—rare earth metals key to the fabrication of advanced technologies.
“The fact that we were able to make it visible here for the first time shows what interesting new phenomena are still to be discovered in the quantum cosmos of materials,” Kai Rossnagel, study senior author and scientist at the DESY Institute in Germany, said in a statement.
Not many, but one
Polarons belong to a family of strange quantum bodies called quasiparticles. Simply put, quasiparticles describe how, under some circumstances, a group of particles will behave collectively as one particle. Polarons characterize the interaction between electrons and atoms, in this case the rare metal compound. The slightly distorted atomic layers drastically slow down the electrons, putting a damper on the flow of electrons—electricity.
These transitions “show that the properties of a material cannot be explained by its chemical composition alone,” noted the researchers in the statement. Electrons tend to be privy to the movements of other electrons nearby and will easily move together as quasiparticles, they added, in the process “forming particle-like states with new properties.”
An odd little bump
The team initially set out to investigate the general properties of the thulium-based compound. They carried out various measurements of the material using different radiation sources, including intense X-rays at particle accelerators. For some reason, they kept seeing a tiny bump next to the main signal.
As per usual, they waved it off as a technical error, but the bump persisted throughout the various measurements. At this point, the researchers decided to embark on a focused investigation of the signal—a project that ended up taking years to complete.
It was when they brought in a 70-year-old model that the calculations finally made sense. Essentially, the small bump was the product of electrons vibrating together with the atoms of the metal compound as a polaron, according to the paper.
“That was the decisive step,” explained Chul-Hee Min, study lead author and a physicist at Kiel University in Germany, in the statement. “As soon as we included this interaction in the calculations, the simulation and measurements matched perfectly.”
What’s more, it’s already known to physicists that many modern quantum materials display similar properties. If researchers can better harness these odd electronic properties, polarons could hasten the arrival of materials such as room-temperature superconductors.
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