Probing non-dipole allowed excitations in highly correlated materials with nanoscale resolution

Here, we demonstrate that non-dipole allowed d–d excitations in NiO can be measured by electron energy loss spectroscopy (EELS) in transmission electron microscopes (TEM). Strong excitations from 3A2g ground states to 3T1g excited states are measured at 1.7 and 3 eV when transferred momentum are beyond 1.5 Å−1. We show that these d–d excitations can be collected with a nanometrical resolution in a dedicated scanning transmission electron microscope (STEM) by setting a good compromise between the convergence angle of the electron probe and the collected transferred momentum. This work opens new possibilities for the study of strongly correlated materials on a nanoscale.