Superkicks and the photon angular and linear momentum density

We address the problem of determining the physically correct definition of the momentum and angular momentum densities in a spatially structured electromagnetic field, given that the expressions are not the same when one uses the canonical energy-momentum tensor instead of the symmetric Belinfante energy-momentum tensor in electrodynamics. This has important consequences for the interaction of matter with structured light, for example, twisted photons, and would give drastically different results for forces and angular momenta induced on small test objects. We show, with numerical estimates of the size of the effects, situations where the canonical and symmetrized forms induce very different torques or (superkick) recoil momenta on small objects or atomic rotors, over a broad range of circumstances.