New study reveals exotic electronic crystals within graphene

TEC at ν = 1/4 of twisted bilayer–trilayer graphene. Credit: Nature (2025). DOI: 10.1038/s41586-024-08239-6
Researchers from the University of British Columbia, the University of Washington, and Johns Hopkins University have identified a new type of quantum state in a custom-designed graphene structure.
The study, published in the journal Nature, reports the discovery of topological electron crystals in twisted bilayer-trilayer graphene. Graphene is a system created by introducing precise rotational twists between stacked two-dimensional materials.
“The starting point for this research is two graphene flakes made up of carbon atoms arranged in a honeycomb structure. The way electrons bounce between carbon atoms determines graphene’s electrical properties, and ultimately “On the surface, it becomes similar to other common conductors like copper,” says Joshua Falk, a member of UBC’s Department of Physics and Astronomy and the Blusson Institute for Quantum Matter. the professor said. QMI).
“The next step is to stack the two flakes with a small twist between them. This creates a geometric interference effect known as a moiré pattern. Some areas of the stack , the carbon atoms of the two flakes overlap directly. In other regions, the atoms are offset,” Falk said.
“When an electron jumps over this moiré pattern of twisted stacks, its electronic properties change completely. For example, the electron slows down significantly and is sometimes twisted in its motion, like the vortex of water in a drain.” The water in the bathtub is flowing out. ”
The breakthrough reported in this study was made by UBC undergraduate Luijen, who is studying twisted graphene samples prepared by Dr. Daysen Waters, a postdoctoral researcher in the lab of Professor Matthew Jankowitz at the University of Washington. Observed by Mr. Sue.
While working on an experiment in Falk’s lab, Ruiheng discovered that the electrons in graphene were frozen into perfectly ordered arrays, locking them in place while allowing a ballet dancer to gracefully perform a stationary pirouette. We discovered a unique configuration of the device, which rotates in unison like this. This synchronous rotation creates a remarkable phenomenon in which current flows smoothly along the edges of the sample, while the interior remains insulated because the electrons are fixed.
Remarkably, the amount of current flowing along the edge is determined precisely by the ratio of two fundamental constants of nature: Planck’s constant and the electron’s charge. The accuracy of this value is ensured by a property of the electronic crystal known as topology. Topology describes the properties of an object that do not change with slight deformation.
“Just as a donut cannot be smoothly transformed into a pretzel without first cutting it open, the circulation channels of electrons around a bounded 2D electron crystal remain undisturbed by the disorder of the surrounding environment.” said Jankowitz.
“This leads to a paradoxical behavior in topological electron crystals not seen in traditional Wigner crystals of the past. Although the crystal freezes electrons to form ordered arrays, it can be conducted.”
An everyday example of topology is the Möbius strip, a simple but evocative object. Imagine making a loop of paper and taping the ends. Then take out another strip. But before joining the ends, give them one twist. The result is a Möbius strip, a surface with only one side and one edge. Surprisingly, no matter how you try to manipulate the strip, you can’t untwist it back into a normal loop without tearing it.
The rotation of electrons in the crystal resembles the twisting of a Möbius strip, and is a hallmark of topological electron crystals that has not been seen before in the rare cases in which electron crystals have been observed: edges where electrons flow. Connect. It is described as being fixed within the crystal itself without any resistance.
Topological electron crystals are not only attractive from a conceptual point of view, but also offer new opportunities for advances in quantum information. These include future efforts to combine topological electron crystals with superconductivity to form the basis of qubits in topological quantum computers.
Further information: Ruiheng Su et al. Moiré-driven topological electron crystals in twisted graphene, Nature (2025). DOI: 10.1038/s41586-024-08239-6
Provided by University of British Columbia
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