Universal Topological Electronic Properties of Nonmagnetic Chiral Crystals

Chiral crystals are materials whose lattice structure has a well-defined handedness due to the lack of inversion, mirror, or other roto-inversion symmetries. Their structural chirality has been found to allow a wide range of phenomena, including skyrmions in chiral magnets, unconventional pairing in chiral superconductors, nonlocal transport and unique magnetoelectric effects in chiral metals. We show a universal topological electronic property of all nonmagnetic chiral crystals with spin-orbit coupling. In these materials, the combination of structural chirality and time-reversal symmetry is sufficient to guarantee the presence of two-fold-degenerate chiral fermions at the time-reversal invariant momenta, Kramers-Weyl. We further show that Kramers-Weyl fermions enable a number of unique topological phenomena, including a quantized photogalvanic current, the chiral and gyrotropic magnetic effects and electron spin-momentum locking. Considering the abundance of chiral crystals, our findings are widely applicable. The symmetry-guaranteed presence of these fermions in all chiral crystals provides a new and reliable means of engineering and controlling the unconventional optical, transport, and superconducting properties of chiral materials[1].
1.G. Chang et al., arXiv: 1611.07925