A crystal takes on an unusual topology

A Möbius strip has a peculiar geometry, but anyone can make one with a strip of paper. Put a half-twist in the strip and tape its ends together, and a single-surface curiosity is born.

WITH A TWIST. A single-crystal Möbius strip (top micrograph) forms when a crystal ribbon grows around a selenium droplet (bottom illustration). Nature

Making a Möbius strip out of paper is one thing, but now a team of Japanese researchers has found a way to coerce a single crystal into the same shape.

Satoshi Tanda of Hokkaido University and his colleagues grew crystals of NbSe3, which contains niobium and selenium, on the surface of droplets of selenium. Single ribbons of the crystal grew around drops’ equators, forming rings. Sometimes, however, a growing ribbon twisted 180, making the ring a Möbius strip.

This probably happened for a couple of reasons, says Tanda, who reported the results with his colleagues in the May 23 Nature. For example, if the crystal isn’t growing exactly on the droplet’s equator, the ribbon is subject to forces that bend it. Meanwhile, the rotation of the selenium drop might contribute to the half twist.

Tanda says the NbSe3 Möbius strips and other crystals with unusual topologies, such as one in the shape of a figure eight, provide novel frameworks for studying quantum mechanical phenomena. He also hints that the structures could lead to new microscopic devices.

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