BERKELEY, September 18 — A research team led by the US Department of Energy’s Lawrence Berkeley National Laboratory has developed an approach that let it directly observe how electrons interact with defects in advanced semiconductor devices, at a level of detail the lab describes as unprecedented. The work, published in the journal Nature, centres on two-dimensional semiconductors — materials just a single layer, or a few layers, of atoms thick — whose ultrathin structure changes how electrons behave.
The technical reality here is that 2D materials can host electron states that simply do not turn up in the bulk silicon the industry has spent decades optimising. Berkeley Lab’s team investigated 2D materials in which electrons sit in an unusual state known as a Wigner solid.
Why a Wigner solid changes the rules
In ordinary semiconductor devices, electrons behave largely like independent particles moving through the material. Their interactions with one another exert a relatively minor influence on their behaviour, and on how the device as a whole operates. Mike Crommie, a senior faculty scientist in Berkeley Lab’s Materials Sciences Division and professor of physics at UC Berkeley, and one of the study’s authors, put it in terms physicists tend to reach for.
“Physicists call this conventional state a Fermi liquid because the electrons move around like waves in the ocean,” he said. Under certain conditions, electrons can instead enter a Wigner solid state, in which they separate from one another and become immobile.
Physicists describe such a system as “strongly interacting” because the electrons’ mutual repulsion becomes the dominant factor shaping their behaviour. Rather than moving independently, they organise themselves into a relatively orderly pattern and behave collectively as a group. That collective behaviour is precisely what makes the system hard to interrogate.
Historically, it has not been possible for scientists to directly image how electrons and defects interact in strongly interacting 2D semiconductor systems. Designing a semiconductor device that can be imaged with enough resolution to resolve features on the scale of individual atoms is extremely difficult.
Researchers have therefore often resorted to a less direct approach: connecting wires to semiconductor devices and measuring how easily electricity flows through them. Crommie was blunt about the limits of that method. “Some of the conclusions in these previous experiments were ambiguous because the researchers could not actually see the electrons and the defects at the same time,” he said.
“They were inferring the behavior based on electrical conductivity.”
The simulation tool under the hood
What distinguishes this effort is the pairing of experiment with theory. The team’s methodology included an innovative simulation tool that enabled accurate theoretical interpretations of their experimental observations — the piece that turns a striking image into a defensible physical claim. As ever, the detail that matters is not the picture itself but whether the model behind it holds up.
Crommie framed the result as a foundation rather than an endpoint. “Our study yielded valuable insights into why electrons in 2D semiconductors behave the way they do,” he said.
“Our methods open the door to the discovery of never-seen-before electron behaviors that can be used for new semiconductor capabilities. This will be important for the future development of semiconductor devices at the ultimate limits of miniaturization.” The team was not Berkeley Lab alone.
Other members include Feng Wang, a faculty senior scientist in the lab’s Materials Sciences Division and a professor in UC Berkeley’s Department of Physics, alongside scientists from the University of California, the Flatiron Institute, the University of New Mexico, Hofstra University, Arizona State University, and the National Institute for Materials Science in Japan. Conventional silicon-based devices — transistors, computer chips, sensors — are built from materials whose atoms are arranged in three-dimensional structures.
Device developers have increasingly explored 2D semiconductors as an alternative, precisely because the ultrathin geometry alters electron behaviour in ways that could unlock new capabilities. Watch for two things next. Whether the simulation tool travels beyond this collaboration, since a method that reliably interprets strongly interacting systems is worth more than any single result.
And whether the electron behaviours Crommie describes as never-seen-before turn out to be engineerable — the point at which a physics curiosity becomes a device roadmap.
