MIT physicists have made an exciting discovery: in an ultra-thin material, electrons can form crystal-like structures, acting like tiny frozen blocks of energy.
This unexpected finding adds to a series of groundbreaking discoveries from the same material, which the team first identified three years ago.
In a new study published in Nature, researchers found that by adjusting the voltage in specially designed devices and cooling them to temperatures near outer space conditions, electrons could behave in unusual ways.
Under these extreme conditions, the electrons in the material turned into a solid-like structure, similar to ice forming from water.
At the same time, the scientists also discovered two new states of matter, building on their previous work that showed electrons could split into fractions of themselves.
A Mysterious New Material
The material behind these discoveries is called rhombohedral pentalayer graphene, which is essentially a special form of graphene, a material made of ultra-thin layers of carbon.
You can think of it as an advanced version of the graphite found in pencil lead.
Since first identifying this material, the MIT team, led by Assistant Professor Long Ju, has experimented with ways to enhance its properties. One key breakthrough came in 2023 when they created a “sandwich” with layers of hexagonal boron nitride acting as the outer layers. By applying different voltages to this setup, they uncovered new electronic behaviors never before seen in natural graphite.
One of their most surprising findings last year was that electrons in the material could split into fractions—a phenomenon known as the fractional quantum Hall effect. Normally, this effect requires strong magnetic fields, but Ju’s team showed that it could happen in their material without any magnets. Because of this, they called it the fractional quantum anomalous Hall effect (“anomalous” means it happens without a magnetic field).
New Breakthroughs: Electrons Turn to Ice
Now, in their latest research, the team has discovered even more surprising behaviors. By cooling the material to an extremely low temperature of 30 millikelvins (almost -460°F), they found two new fractional states of electrons.
But even more exciting was the discovery of a new “solid” phase of electrons. While last year’s findings showed that electrons could act like a flowing liquid, this new research revealed that under certain conditions, they could also freeze into a crystal-like structure—similar to how water turns to ice.
Ju explains that the relationship between these two phases is like a map of rivers and glaciers: the flowing electron “liquid” (representing the fractional states) carves paths through frozen electron “ice” (representing the solid-like integer effect). This suggests that the material contains an even richer variety of states than previously imagined.
Even more promising is that these discoveries were observed in both five-layer and four-layer versions of rhombohedral graphene. This suggests there may be a whole family of similar materials with these remarkable properties waiting to be explored.
“This work shows just how exciting and exotic this material is,” said researcher Zhengguang Lu, now a professor at Florida State University. “We’re only just beginning to uncover its full potential.”
With each new experiment, MIT physicists continue to reveal astonishing behaviors in this ultra-thin material. Who knows what other surprises are hidden within?
