Single pair of Weyl fermions in the half-metallic semimetal EuCd2As2

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 EuCd 2 As 2 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 EuCd 2 As 2 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 G 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.

Topological magnetotorsional effect in Weyl semimetals

“…This remarkable relation has the same universal form in all Weyl materials and is independent on the specific spatial profile of the magnetic texture. We discuss how this relation can be experimentally probed in magnetic Weyl material EuCd 2 As 2 [11][12][13].…”

Unconventional Transverse Transport above and below the Magnetic Transition Temperature in Weyl Semimetal EuCd2As2

“…It has been demonstrated recently that the antiferromagnet EuCd 2 As 2 with T N ∼ 9.5 K would be an ideal candidate for the study of the interplay between magnetism and topology, as it exhibits various topological states in both the antiferromagnetic (AFM) and paramagnetic (PM) phases [23][24][25][26][27][28]. In the AFM phase, depending on the direction of the Eu magnetic moments, various nontrivial topological ground states have been predicted, such as magnetic topological Dirac semimetal, or axion insulator, AFM topological crystalline insulator, and higher order topological insulator [27].…”

Detection of Fermi arcs in Weyl semimetals through surface negative refraction

“…The space-resolved peak structure of the nonlocal conductance which indicates the trajectory of negative refraction can serve as unique evidence of the Fermi arc states. Recent progress on Weyl semimetals with a single pair of Weyl nodes in MnBi 2 Te 4 [42] and EuCd 2 As 2 [43,44] paves the way for the realization of our proposal. Furthermore, the manipulation of the negative refraction process offers potential applications of a Weyl semimetal nanowire as a field-effect transistor [40].…”

“…In reality, there are only a few material candidates for Weyl semimetals with only two Weyl points [42][43][44]. Hence, we investigate negative refraction between the surface states of T -symmetric Weyl semimetals, which are more abundant [12][13][14][15][16].…”

“…As a result, part of the scattering channels at the Fermi energy level is absent, serving as a source for unique transport properties, including negative refraction between different surfaces [41]. In reality, the electronic transport signatures will depend on the material details and their specific termination, both of which affect the Fermi arcs' orientation, dispersion, and length [12][13][14][15][16][17][42][43][44]. Notably, however, stateof-the-art fabrication techniques allow for controlled surface shaping on the level of a single layer [16,18,45,46], making it possible to explore the broad breadth of surface transport phenomena.…”