First measurement of the Anomalous Hall effect of a light beam

Researchers from Cnr-Nanotec in Lecce have demonstrated in a work published on Nature that a photon beam can drift laterally from its trajectory due to the topological curvature of its energy band, like if rolling on a cliff it could feel a different wind depending on its polarization state.

Everybody knows that electrons in any material can be dragged by an electric field acting on their charge, while a magnetic field, instead, make them deviate orthogonally to the electrons trajectory (Hall effect). This is the essence of electrodynamics, but it’s not the whole story. In the case of crystals, for instance, the geometric properties or more precisely the topology of the energy bands (the electronic bands, the set of energies and velocities that electrons can acquire at the interior of a material) do influence their movement, allowing for very interesting effects such as the observation of the well-known quantum Hall effect, where the trajectory of the electron is bent laterally as in the presence of an “artificial magnetic field”. Read more here.