Negative Cherenkov emission
A relativistic electron bunch (represented by the spheres in red scale) propagates in a negatively refracting metamaterial exciting Cherenkov radiation (represented by the magnetic field isosurfaces in blue).
The unusual characteristics of electromagnetic waves in negative index metamaterials, namely the antiparallel phase and group velocities, lead to the formation of reversed Cherenkov radiation cones that point away from the electron bunch.