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Theory of Weyl orbital semimetals and predictions of several materials classes

Graphene, topological insulators, and Weyl semimetals are three widely studied materials classes which possess Dirac or Weyl cones arising from either sublattice symmetry or spin-orbit coupling. In this work, we present a theory of a new class of bulk Dirac and Weyl cones, dubbed Weyl orbital semimetals, where the orbital polarization and texture inversion between two electronic states at discrete momenta lend itself into protected Dirac or Weyl cones without spin-orbit coupling. We also predict several families of Weyl orbital semimetals including V$_3$S$_4$, NiTi3S6, BLi, and PbO$_2$ via first-principle band structure calculations. We find that the highest Fermi velocity predicted in some of these materials is even larger than that of the existing Dirac materials. The synthesis of Weyl orbital semimetals will not only expand the territory of Dirac materials beyond the quintessential spin-orbit coupled systems and hexagonal lattice to the entire periodic table, but it may also open up new possibilities for orbital controlled electronics or `orbitronics'.