In the 127 years since the electron was discovered, it has undergone more scrutiny than perhaps any other particle. As a result, its properties are not just well known, but rote, textbook material: Electrons have a smidgen of mass and negative electric charge. In a conductor, they swim relatively unimpeded as a current; in an insulator, they barely move.
Over time, caveats have cropped up. Under an intense magnetic field, for example, electrons can lose their individual identities and form “quasiparticles”: collective entities, like the shape formed by a school of fish. But even these collective states have been well cataloged.
So it came as a shock last year when a new effect was seen in electrons. Researchers at the University of Washington reported in August 2023 that in a stack of two atomically thin crystalline sheets offset from each other at a slight angle, electrons behaved like quasiparticles with fractional amounts of charge, such as −⅔ and −⅗. A few months later, a team at the Massachusetts Institute of Technology reported the same effect in another material. It was the first time that electrons had formed fractional quasiparticles without the enabling influence of a magnetic field.
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