The phase and the group velocity of light propagating in conventional optical media cannot exceed the speed of light in vacuum. However, in so-called epsilon-near-zero (ENZ) materials, light exhibits ...

Singularities of many kinds arise in nearly every branch of physics, from dislocations in crystals 9 and flux quanta in superconductors 1 to vortex cores in fluid flows (for example, cyclones) and ...

IN all smooth wave-guides and many loaded wave-guides the phase velocity has the same sign as the energy velocity. Some systems having complex forms of loading have in the past been attributed with ...