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Suchitra Sebastian is a fringe physicist. Not a crackpot — she lectures at the University of Cambridge and has published a string of papers in Science and Nature. But she likes to venture into the borderlands between forms of matter that other physicists have already explored. There, in the liminal space where the particles in a material begin to change from one configuration to another, new quantum effects appear. “A lot of it is really exciting phenomena that emerges before it’s theoretically predicted,” Sebastian said with delight.

Last year, she and her colleagues discovered what appeared to be electrons looping their way through an insulator, a type of material that by definition prevents such movement. The observation, in a substance called samarium hexaboride, is still not understood. But Sebastian says one possibility is that what was looping was not electrons but an entirely new kind of subatomic building block.

Interactions between electrons create wavelike disturbances — known as quasiparticles — that serve as the basic components of almost every complex material. The known quasiparticles tend to act like heavier versions of electrons, but not so in this case. “In samarium hexaboride, the possibility is that the electron itself has broken apart,” said Sebastian. “So instead of thinking of the electron as the building block, we would need to think of fractional parts of the electron as building blocks.” These fractional quasiparticles would create an entirely new way to understand the universe of materials.

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