It was only a matter of time.

A weird form of matter called a time crystal has made an appearance in two more types of materials, doubling the number of known time crystal habitats. In a typical crystal, its arrangement of atoms regularly repeats in space, such as the alternating sodium and chloride ions that make up a salt crystal. But time crystals’ patterns repeat themselves at regular time intervals. 

A team of scientists created a time crystal in a solid material called monoammonium phosphate, the researchers report in both the May 4 Physical Review Letters and the May 1 Physical Review B. Another team made its time crystal in a type of liquid containing star-shaped molecules, according to a study also published in the May 4 Physical Review Letters.

Both time crystals rely on a quantum property called spin, which makes some atomic nuclei seem to whirl like a top. In the time crystals, the direction of that spin flipped at regular intervals.

Repeated radio wave pulses were used to trigger the spins’ flip-flopping. But even when the spins weren’t flipped perfectly, both materials kept up a regular pattern of flipping, revealing that they had a preferred time structure.

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