Time crystals – structures whose lowest- energy configurations are periodic in time rather than space – were first experimentally demonstrated in 2017 in (spatially) disordered systems. Two independent teams have now added spin systems periodically driven by NMR pulses to the list of systems that can host time crystals. Jared Rovny and colleagues of Yale University used radio-frequency (RF) pulses to periodically rotate the spins of phosphorus-31 nuclei inside a crystal of ammonium dihydrogen phosphate, finding that the spins displayed time-crystal behaviour, oscillating at twice the period of the pulse sequence. In a distinct NMR experiment, Soham Pal and colleagues at the Indian Institute of Science Education and Research found time-crystal behaviour in a liquid, using molecules with a central spin surrounded by several satellite spins and subjecting the molecules to an RF pulse sequence.

Further reading

J Rovny et al. 2018 Phys. Rev. Lett. 120 180603; Phys. Rev. B 97 184301.
S Pal et al. 2018 Phys. Rev. Lett. 120 180602.