Effect of Deformation on Topological Properties of Cobalt Monosilicide

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.

Strain-induced topological charge control in multifold fermion systems

“…Our Hamiltonian should be such that it commutes with the screw operators but does not commute with the three-fold rotational operator, S 3 . In order to incorporate the effect of strain, we use the strain tensor introduced in reference [88], which acts as a perturbation on the unstrained Hamiltonian. Biaxial strain in the xy plane can, in effect, be modeled by a uniaxial strain along the z direction.…”

Hawking fragmentation and Hawking attenuation in Weyl semimetals

“…In solids, the preparation of a controlled tilt profile is a key challenge. Possible solutions are carefully designed strain patterns [30,59,[80][81][82][83][84][85][86], and multilayer systems with specific inter-layer tunnelings [87,88]. In addition, the presence of additional states in three-dimensional solid or metamaterial analogues will generically impede the detection of Hawking fragmentation and Hawking attentuation.…”

Strain-induced topological charge control in multifold fermion systems

“…In order to incorporate the effect of strain, we use the strain tensor introduced in Ref. 88 , which acts as a perturbation on the unstrained Hamiltonian. Biaxial strain in the xy plane can, in effect, be modelled by a uniaxial strain along the z direction.…”