Abstract
Recently, it was shown that materials with certain crystal structures can exhibit multifold band crossings with large topological charges. CoSi is one such material that belongs to non-centrosymmetric space group P213 (#198) and posseses multifold band crossing points with a topological charge of 4. The change of crystal symmetry, e.g., by means of external stress, can lift the degeneracy and change its topological properties. In the present work, the influence of uniaxial deformation on the band structure and topological properties of CoSi is investigated on the base of ab initio calculations. The k·p Hamiltonian taking into account deformation is constructed on the base of symmetry consideration near the Γ and R points both with and without spin-orbit coupling. The transformation of multifold band crossings into nodes of other types with different topological charges, their shift both in energy and in reciprocal space and the tilt of dispersion around nodes are studied in detail depending on the direction of uniaxial deformation.
Highlights
Cobalt monosilicide crystallizes in the cubic noncentrosymmetric space group #198(P21 3)
Earlier calculations [3,4] without the account of spin-orbit coupling (SOC) revealed the presence of multiple band crossings at the Γ and R points of the Brillouin zone, but they did not consider the topology of the band structure
The symmetry analysis allowed to predict the existence of chiral fermions and multifold band crossings with high topological charges in crystals belonging to several space groups in the presence of time-reversal symmetry [16,17]
Summary
Cobalt monosilicide crystallizes in the cubic noncentrosymmetric space group #198(P21 3). Band structures calculated with and without the account of spin-orbit coupling (SOC) are plotted in Figure 1c,d, respectively. Earlier calculations [3,4] without the account of SOC revealed the presence of multiple band crossings at the Γ and R points of the Brillouin zone, but they did not consider the topology of the band structure. The symmetry analysis allowed to predict the existence of chiral fermions and multifold band crossings with high topological charges in crystals belonging to several space groups (including space group #198) in the presence of time-reversal symmetry [16,17]. In CoSi, multifold linear band crossing and spin texture was initially investigated around the Γ point, based on firstprinciple fully-relativistic calculations [5]. It was shown that multifold nodes have large topological charges of ±2 even without SOC
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