# A Single Pair of Weyl Fermions in Half-metallic EuCd2As2 Semimetal

## TL;DR

This paper predicts that EuCd2As2, when ferromagnetically ordered, can host a single pair of Weyl points due to its half-metallic nature, offering a new route to ideal Weyl semimetals without external magnetic fields.

## Contribution

It demonstrates through first-principles calculations that ferromagnetism in EuCd2As2 creates a single pair of Weyl points, advancing the design of ideal Weyl semimetals.

## Key findings

- Inducing ferromagnetism in EuCd2As2 generates a single pair of Weyl points.
- Alloying with Ba stabilizes ferromagnetism and Weyl points without magnetic fields.
- The Weyl points are near the zone center and can be manipulated via magnetic order.

## Abstract

An ideal Weyl semimetal with a single pair of Weyl points (WPs) may be generated by splitting a single Dirac point (DP) through the breaking of time-reversal symmetry by magnetic order. However, most known Dirac semimetals possess a pair of DPs along an axis that is protected by crystalline symmetry. Here, we demonstrate that a single pair of WPs may also be generated from a pair of DPs. Using first-principles band structure calculations, we show that inducing ferromagnetism in the AFM Dirac semimetal EuCd2As2 generates a single pair of WPs due to its half-metallic nature. Analysis with a low-energy effective Hamiltonian shows that this ideal Weyl semimetal is obtained in EuCd2As2 because the DPs are very close to the zone center and the ferromagnetic exchange splitting is large enough to push one pair of WPs to merge and annihilate at Gamma while the other pair survives. Furthermore, we predict that alloying with Ba at the Eu site can stabilize the ferromagnetic configuration and generate a single pair of Weyl points without application of a magnetic field.

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Source: https://tomesphere.com/paper/1901.08234