Title: Type-II Dirac Photons,
Abstract: The Dirac equation for relativistic electron waves is the parent model for
Weyl and Majorana fermions as well as topological insulators. Simulation of
Dirac physics in three-dimensional photonic crystals, though fundamentally
important for topological phenomena at optical frequencies, encounters the
challenge of synthesis of both Kramers double degeneracy and parity inversion.
Here we show how type-II Dirac points---exotic Dirac relativistic waves yet to
be discovered---are robustly realized through the nonsymmorphic screw symmetry.
The emergent type-II Dirac points carry nontrivial topology and are the mother
states of type-II Weyl points. The proposed all-dielectric architecture enables
robust cavity states at photonic-crystal---air interfaces and anomalous
refraction, with very low energy dissipation.