Chirality flip of Weyl nodes and its manifestation in strained MoTe$_2$

TL;DR

This paper reveals a novel process where the topological charge of Weyl nodes in topological semimetals can flip sign through the merging of three nodes, influenced by symmetry constraints, with implications for strained MoTe$_2$.

Contribution

It demonstrates a new chirality flip mechanism involving three Weyl nodes, expanding understanding of topological charge dynamics under symmetry constraints.

Findings

Chirality of Weyl nodes can change sign via merging of three nodes.

Strain in MoTe$_2$ can induce this chirality flip near the Fermi level.

Transport properties can distinguish this process from conventional Weyl merging.

Abstract

Due to their topological charge, or chirality, the Weyl cones present in topological semimetals are considered robust against arbitrary perturbations. One well-understood exception to this robustness is the pairwise creation or annihilation of Weyl cones, which involves the overlap of two oppositely charged nodes in energy and momentum. Here we show that their topological charge can in fact change sign, in a process that involves the merging of not two, but three Weyl nodes. This is facilitated by the presence of rotation and time-reversal symmetries, which constrain the relative positions of Weyl cones in momentum space. We analyze the chirality flip process, showing that transport properties distinguish it from the conventional, double Weyl merging. Moreover, we predict that the chirality flip occurs in MoTe$_2$, where experimentally accessible strain leads to the merging of three Weyl cones close to the Fermi level. Our work sets the stage to further investigate and observe such chirality flipping processes in different topological materials.