A team of physicists announces having created a new exotic state of matter, known as Rydberg’s polarons. This state is formed at ultra-cold temperatures, when an electron orbits its nucleus at a distance so great that other atoms eventually bind within the orbit.
Matter is composed of atoms whose nucleus is surrounded by one or more electrons. Generally, between the nucleus of an atom and the electrons that surround it, you will only find a void. But nature hates emptiness. Thus, when electrons get too far away, it sometimes happens that other atoms get trapped inside the orbit of the last electron, resulting in a new state of matter.
The idea, theorized by researchers from the University of Vienna in Austria, and the University of Havard in the United States, has been confirmed by an American team from Rice University.
The researchers say they first created a Bose-Einstein condensate from strontium atoms at temperatures near absolute zero. Then, using a laser, they transformed an atom of the condensate into a Rydberg atom. “The average distance between the electron and the nucleus of a Rydberg atom can be up to several hundred nanometers, which is more than a thousand times the radius of a hydrogen atom,” explains physicist Joachim Burgdörfer from the University of Vienna. Here, the radius of the orbit borrowed by this electron is then much larger than the average distance between two atoms of the condensate. Thus, up to 170 strontium atoms were able to lodge in the Rydberg atom. An atom stuffed with atoms, literally.
You can see an illustration of this “atom giant” filled with atoms below – the blue represents the electron and the interior of its orbit, the nucleus is here in red, and inside the blue zone is found a group of other atoms represented in green.
The big question then was how, in this unusual embrace, these atoms could influence each other, if at all.
“Atoms do not carry any electric charge, so they only exert minimal force on the electron,” says physicist Shuhei Yoshida. The weak interactions between this electron and these atoms then only very slightly decrease the total energy of the system. Such a drop in energy could theoretically establish a weak bond between the Rydberg atom and the other strontium atoms sitting quietly in the orbit of its electron – the so-called Rydberg polarons. This new exotic state of matter can only persist at extremely low temperatures.