Physicists say they've discovered a new particle with a Jekyll-and-Hyde personality, capable of behaving like both matter and antimatter.
In the early days of the 20th century, when quantum theory began to be formulated, it was assumed most particles such as electrons and others should have strange "antimatter" counterparts of the identical mass but with an opposite charge.
Two such particles, one matter and one antimatter, should annihilate each other if they came in contact with each other, theorists said.
However, in 1937 Italian physicist Ettore Majorana hypothesized a single stable particle dubbed the "Majorana fermion" that could serve as either matter or antimatter, existing as its own "antiparticle."
It would have no electrical charge, and could therefor exist as a particle and an antiparticle that are completely identical.
The hunt for that elusive particle has been underway ever since.
Now, scientists at Princeton University and the University of Texas at Austin say they've captured an image of a particle they suggest is the long-sought Majorana fermion.
Placing a long thin chain of magnetic iron atoms on a superconducting base of lead, they examined the two materials with a scanning-tunneling microscope.
An electrically neutral signal at each end of the iron chain, assumed to be a "key signature" of a Majorana fermion, was detected, they reported in the journal Science.
The fermion showed up in exactly the location that decades of study and calculation suggested it would, the researchers say.
It was predicted that under optimum conditions, a Majorana fermion would emerge at each end of such a superconducting wire.
They would be stable and would not annihilate each other -- unless the wire out off which they emerged was too short -- because of their spatial separation, the hypothesis suggested.
The experiment exactly followed what was expected from the theory, the researchers said.
"This is the most direct way of looking for the Majorana fermion as it is expected to emerge at the edge of certain materials," physicist and study leader Yazdani says. "If you want to find this particle within a material you have to use such a microscope, which allows you to see where it actually is."
While the experimental setup demonstrating the existence of Majorana particle is very complex, he says, it does not use exotic materials and so will be easy for other researchers to reproduce and study.
"What's very exciting is that it is very simple: it is lead and iron," he said.
While it is important to a fundamental understanding of particle physics, he said, it would likely also lead to practical uses "because it allows scientists to manipulate exotic particles for potential applications, such as quantum computing."