Nature Commun. 5, 4441 (2014)

Spontaneous chiral symmetry breaking is a phenomenon that is at the core of the existence of our universe as it is today. It determined the fact that fundamental particles indeed have a mass and what their mass is. Spontaneous symmetry breaking consists of the 'hiding of symmetry' of a particular physical system, whose underlying laws and initial state are invariant under a particular symmetry transformation, during its evolution. By changing an external parameter, the system evolves to an asymmetric state, which does not retain the initial symmetry that remains hidden in its governing laws. Now Yuri Kivshar and collaborators have demonstrated this effect in chiral magnetoelastic metamaterials comprising enantiomeric units. The asymmetry is observed in the acquisition of a non-zero polarization rotation of the forward-scattered wave during a microwave pump–probe experiment, when the pump power is increased. This effect creates an artificial phase transition from an achiral to a chiral response. This study opens the way to the ad hoc design of metamaterials with artificial phase transitions, such as those that go from a positive to negative index and from elliptic to hyperbolic dispersion.