The electronic properties of materials are typically determined by their structure under normal, undisturbed conditions, when they are in a state known as equilibrium. Intense light beams, however, can temporarily reshape a material’s electronic band structure (i.e., the range of energy states available to electrons), potentially giving rise to new electronic behaviors.

Researchers at Friedrich-Alexander University Erlangen-Nürnberg, Ludwig Maximilian University of Munich, the Technion—Israel Institute of Technology, and the University of Central Florida recently demonstrated that illuminating graphene with a specific type of light temporarily modifies its electron states, prompting the emergence of a so-called Floquet topological insulator.

This is a transient, out-of-equilibrium state created when a periodically oscillating field reshapes a material’s electronic structure, resulting in topological properties that are absent at equilibrium.