This Bizarre Particle Can Completely Change Its Physical Properties
For 16 years, scientists hypothesized the existence of a quasi-p called a semi-Dirac fermion, named after mathematician Paul Dirac whose eponymous equation describes these fermions.
Now, a new study claims to have spotted these ps in a semimetal material, which conducts electricity like a normal material but exhibits quantum behavior under extreme conditions.
They found that these ps are massless when influenced by magnetic fields flowing a particular direction, but then gain mass when that direction changes.
The subatomic world is home to many mysteries in both quantum and classical physics. It's well known that ps act strangely as they cool down to absolute zero and begin to exhibit quantum effects. For some ps, this can induce superconductivity—where an electrical current could theoretically exist forever due to a lack of resistance. For other ps, such as semi-Dirac fermions, it means fluctuating mass depending on the direction of magnetic fields.
This is the conclusion of a forthcoming paper, accepted by the journal Physical Review X , that reports the first instance of these theorized ps in semimetals ("semi" because they conduct electricity like metals except under extreme conditions). When these semi-metals were subjected to supercold—approaching-absolute-zero— temperatures, the researchers noticed that the ps didn't flow forward normally, but instead formed circular movements like eddies in a river. And staying true to the maxim of ' absolute zero does funky things to matter,' the material exhibited quantum effects that made the ps act "like a wave that self-reinforced as it flowed around the eddy," according to New Scientist .
To make sure they were indeed analyzing the hypothesized semi-Dirac fermion, the research team subjected the semimetal to various magnetic fields and light frequencies in order to identify the p . However, the strangest behavior they witnessed was when the team redirected magnetic fields in relation to the ps themselves.
"This [p] is very bizarre ," Yinming Shao told New Scientist. "You can imagine walking on the streets of New York and if you go straight, you are super light, you are massless. But turn 90 degrees east or west, and you become super massive."
The team used infrared light to analyze the p by the light it reflected back—an extremely difficult process, as semimetals contain many other ps that reflect infrared as well. These quasi-ps are particularly interesting because they exist in a middle ground between the normal electrons in metals and the kind of massless neutrinos that flow throughout the cosmos. Further study of these ps could help reveal new insights into a variety of physics, including Coulomb interactions and other quantum phenomena.
For 16 years, scientists searched for this hypothetical p. And now that it's been observed, there's lots to learn.
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