Exceptional Point Dynamics in Photonic Honeycomb Lattices with PT   Symmetry
  We theoretically investigate the flow of electromagnetic waves in complex honeycomb photonic lattices with local PT symmetries. Such PT structure is introduced via a judicious arrangement of gain or loss across the honeycomb lattice, characterized by a gain/loss parameter \gamma. We found a new class of conical diffraction phenomena where the formed cone is brighter and travels along the lattice with a transverse speed proportional to Sqrt (\gamma). 
Hamidreza Ramezani, Tsampikos Kottos, Vassilios Kovanis, Demetrios N.   Christodoulides
physics.optics quant-ph