Strain induced Kramers-Weyl Fermions

Kramers-Weyl fermions are recently found to be widely supported in chiral crystals and exhibit many novel properties. However, in achiral crystals due to the presence of mirror or roto-inversion symmetries, Kramers Weyl fermions are often obscured to emerge due to the presence of nodal lines. In this work, we show Kramers-Weyl fermions are easily generated by removing the degeneracy of these nodal lines through strain effects. Remarkably, based on realistic DFT calculations, in the strained Rashba semiconductor BiTeI, we find a single Kramers-Weyl fermion near Fermi energy. Moreover, a strain induced quantized circular photogalvanic effect (CPGE) is further established. Our work paves a way to study the topology, optoelectronics by the tuning the chirality of crystals.