Fig. 4: Origin of chirality-locking, unidirectional CDW in CoSi.
From: Chirality locking charge density waves in a chiral crystal
a Atomic structure of the four sub-layers in a unit cell of CoSi. b Top view of the first and second sublayers. The red line outlines the electron hopping path of Co_1-Co_2-Si_2-Si_1-Co_1-Co_2…. The gray line outlines another path following the same atomic sequence in the two-sublayer model. These two paths are inequivalent with each other in bulk CoSi. c Large-scale STM image showing coexistence of two different crystal enantiomers separated by a domain boundary. The blue and green dashed lines highlight the CDW stripes of enantiomers 1 and 2, respectively. The CDW orders are unidirectional in both enantiomers, but their CDW wave vectors point to different directions respectively. Atomic structures of crystal enantiomers 1 (d) and 2 (g). DFT revealed constant-energy contours of the Fermi surface at the adjusted Fermi level of enantiomers 1 (e) and 2 (h). These contours are only distributed around the Г point in the k-space and the CDW was observed on the x-y plane of the crystal, thus, a slab at kz = 0 with a range of ±0.25 π/a was plotted. Derived JDOS plots, with numerically enhanced contrast, of the DFT Fermi surface contours of enantiomers 1 (f) and 2 (i). The blue (f) and green (i) arrows mark the experimentally observed CDW wave vectors in both direction and amplitude for enantiomers 1 and 2, respectively. The atomic structures, energy contours and JDOS of the two enantiomers show mirror symmetry with each other.
