Enantiomorph conversion in single crystals of the Weyl semimetal CoSi

Chiral intermetallic phases may show unusual chemical and physical properties with nontrivial structure-property relationship. It is therefore of particular interest to study the structural conversion between domains of different handedness. Here, the atomic decoration of the enantiomorph exchange area within single crystal of the Weyl semimetal CoSi is determined by a combination of atomic-resolution scanning transmission electron microscopy imaging, single crystal X-ray diffraction and quantum chemical analysis of atomic interactions. Two-atomic [CoSi] units are shown to be the bonding base for the FeSi-type structure and may be considered as 'pseudo-molecules', thinking of molecular organic crystals. Tiny reorganisation of atomic interactions within these units results in the appearance of sequence 'faults' in the structure pattern i.e. in a different structural motif in the enantiomorph exchange area, which - contrary to the A and B enantiomorphs of CoSi - contains an inversion centre and allows a local enantiomorph 'conversion'. Due to the special features of atomic interactions, the reorganisation of multi-atomic bonds leads to slightly higher total energy. This appears within one and the same grain which is prepared by the short distance chemical vapor transport. Materials with a chiral crystal structure are of great interest due to potentially non-trivial structure-property relations. Here, electron microscopy and crystallographic analysis, supported by quantum chemical calculations, shed light on the conversion of the crystal structure of CoSi accompanying a change in handedness.