Tunable Dual-Type Weyl Points in Dirac-Weyl Semimetal CaAgBi

TL;DR

This paper proposes CaAgBi as a tunable Dirac-Weyl semimetal hosting both Dirac and Weyl fermions, with controllable topological features via alloy engineering and strain, advancing topological spintronics.

Contribution

It introduces CaAgBi as a material with tunable dual-type Weyl points and demonstrates control over their positions and annihilation through alloying and strain.

Findings

Revealed 18 pairs of dual-type Weyl points in CaAgBi.

Confirmed topological features via surface Fermi arcs.

Showed strain and alloy engineering can manipulate Weyl point positions.

Abstract

Dirac-Weyl semimetals host both Dirac and Weyl fermions and the exploration of material candidates with tunable topological properties is essential to realize topological spintronic devices. In this work, we propose CaAgBi as a Dirac-Weyl semimetal with tunable type-I and type-II Weyl points based on first-principle calculations. In addition to the three pairs of Dirac points located along the rotational axis as previously reported, our calculations reveal 18 additional pairs of dual-type Weyl points distributed across three distinct planes: type-I in the $k_z=0$ plane and type-II in the $k_z= \pm 0.0698\,\frac{2\pi}{c}$ planes. The topological features are further confirmed through chirality of the Weyl points as well as the existence of surface Fermi arcs. Moreover, we find that the position and annihilation of Dirac and Weyl points are tunable by the alloy engineering and external strains. The alloy engineering is employed to modulate the positions of Weyl points, revealing different annihilation concentrations for type-I and type-II Weyl points, potentially offering novel experimental strategies for Weyl point manipulation. Under tensile biaxial strain, the Weyl points in the $k_{z}=0$ plane annihilate along the $\Gamma$--$\mathrm{M}$ path at $2.1\%$ strain, whereas the Weyl points in the $k_{z}\neq 0$ planes remain robust within $6\%$ strain. This work provides a versatile platform for manipulating Dirac/Weyl interactions, with spin-orbit coupling (SOC) driven alloy control and strain-selective engineering opening avenues for topological electronics.