Science 363, 148–151 (2019)

Weyl points are singular points of degeneracy in three-dimensional reciprocal (momentum) space at which two energy bands intersect. Such points were experimentally demonstrated in the photonic domain in 2015 and growing interest and applications are now abounding. However, while the fact that Weyl points carry topological charges defined by the Chern numbers has been exploited in other fields of physics, photonics is still lagging. Hongwei Jia and a team from the UK, China and the US have now experimentally observed microwave zero-order Landau levels exhibiting one-way chiral propagation. They achieved this by making designer unit cells of metamaterials that generate an effective gauge field (that is, artificial magnetic field), which was confirmed experimentally and by numerical simulations. Apart from the fundamental nature of the demonstration, the concept, which does not rely on time-reversal symmetry breaking, may allow for means of robust photonic transport that could be useful for information processing and other applications.