# Influence of anisotropy, tilt and pairing of Weyl nodes: The Weyl semimetals TaAs, TaP, NbAs and NbP

## TL;DR

This paper investigates the electronic, spin, and topological properties of four Weyl semimetals, revealing how anisotropy, tilt, and pairing of Weyl nodes influence their physical characteristics and topological invariants.

## Contribution

It provides a detailed analysis of how anisotropy, tilt, and pairing of Weyl nodes affect the electronic structure and topological properties of TaAs, TaP, NbAs, and NbP.

## Key findings

- Weyl bands exhibit strong anisotropy and tilt, especially for W2 nodes.
- Node tilts and positions significantly impact the density of states.
- Pairing of nodes alters spin textures and Berry curvature, indicating topological changes.

## Abstract

By means of $ab \ initio$ band structure methods and model Hamiltonians we investigate the electronic, spin and topological properties of four monopnictides crystallizing in body centered tetragonal structure. We show that the Weyl bands around a Weyl point W1 or W2 possess a strong anisotropy and tilt of the accompanying Dirac cones. These effects are larger for W2 nodes than for W1 ones. The node tilts and positions in energy space significantly influence the density of states of single-particle Weyl excitations. The node anisotropies destroy the conventional picture of (anti)parallel spin and wave vector of a Weyl fermion. This also holds for the Berry curvature around a node, while the monopole charges are independent as integrated quantities. The pairing of the nodes strongly modify the spin texture and the Berry curvature for wave vectors in between the two nodes. Spin components may change their orientation. Integrals over planes perpendicular to the connection line yield finite Zak phases and winding numbers for planes between the two nodes, thereby indicating the topological character.