In a new study published in Nature, physicists at Brown University have discovered a new class of quantum particles known as fractional excitons. These particles behave in surprising ways and have the potential to significantly enhance scientists' understanding of the quantum realm.
A new study finds that new quantum particles form by pairing quasiparticles that carry fractional charges. Image Credit: Demin Liu.
Subatomic particles rarely act according to the laws of the physical world, which is one of the many mysteries of quantum physics. They can simultaneously exist in two locations, transcend solid barriers, and even instantly communicate over vast distances. Although these behaviors might appear unattainable, scientists are investigating previously unthinkable array features in the quantum domain.
Our findings point toward an entirely new class of quantum particles that carry no overall charge but follow unique quantum statistics. The most exciting part is that this discovery unlocks a range of novel quantum phases of matter, presenting a new frontier for future research, deepening our understanding of fundamental physics, and even opening up new possibilities in quantum computation.
Jia Li, Associate Professor, Brown University
In addition to Li, Dima Feldman, a Brown physics professor, and three graduate students, Naiyuan Zhang, Ron Nguyen, and Navketan Batra, conducted the study. The study's co-first authors are Zhang, Nguyen, and Batra.
Building on the classical Hall effect, the team’s research focuses on a phenomenon called the fractional quantum Hall effect, which produces a sideways voltage when an electric current is delivered to a material with a magnetic field. This sideways voltage rises in distinct jumps, as demonstrated by the quantum Hall effect, which happens at very low temperatures and high magnetic fields.
These steps become much more strange in the fractional quantum Hall effect, when they only increase by tiny amounts, carrying a fraction of the charge of an electron.
The researchers constructed a structure in their experiments using two thin layers of graphene, a two-dimensional nanomaterial, and an insulating hexagonal boron nitride crystal. This configuration allowed them to precisely regulate the flow of electrical charges.
It also enabled them to produce particles called excitons, created by fusing an electron with a hole—the lack of an electron. After that, they subjected the system to magnetic forces that were millions of times more powerful than those seen on Earth. The team was able to witness the novel fractional excitons, which displayed a peculiar set of behaviors, thanks to this.
Generally, fundamental particles can be divided into two groups. Since bosons are particles with the same quantum state, many can coexist unhindered. However, a principle known as the Pauli exclusion principle states that no two fermions can occupy the same quantum state.
However, the fractional excitons found in the experiment did not fall neatly into either category. While they had the fractional charges predicted by the experiment, their behavior exhibited the characteristics of both bosons and fermions, operating almost as a hybrid. That made them more similar to anyons, a particle type that exists between fermions and bosons; yet, fractional excitons possessed unique features that distinguished them from anyons.
This unexpected behavior suggests fractional excitons could represent an entirely new class of particles with unique quantum properties. We show that excitons can exist in the fractional quantum Hall regime and that some of these excitons arise from the pairing of fractionally charged particles, creating fractional excitons that don’t behave like bosons.
Naiyuan Zhang, Graduate Student and Study Co-First Author, Brown University
According to the researchers, the discovery of a new class of particles could one day help enhance the way information is stored and handled at the quantum level, resulting in quicker and more reliable quantum computers.
Li added, “We have essentially unlocked a new dimension for exploring and manipulating this phenomenon, and we are only beginning to scratch the surface. This is the first time we’ve shown that these types of particles exist experimentally, and now we are delving deeper into what might come from them.”
The team’s next steps will be to investigate how fractional excitons interact and whether their behavior can be controlled.
This feels like we have our finger right on the knob of quantum mechanics. It is an aspect of quantum mechanics that we didn't know about or, at least, we did not appreciate before now.
Dima Feldman, Professor, Brown University
Journal Reference:
Zhang, N. J., et. al. (2025) Excitons in the fractional quantum Hall effect. Nature. doi.org/10.1038/s41586-024-08274-3