Carrier density dependence of the anomalous Hall conductivity of EuCd₂As₂

Ideal magnetic Weyl semimetals with a single pair of Weyl points close to the Fermi level are highly desirable for realizing the intrinsic topological effects associated with Weyl fermions. The antiferromagnetic layered EuCd₂As₂ was predicted as an ideal Weyl semimetal in the spin polarized ferrimagnetic (FM) state. However, the direct experimental demonstration of the ideal FM Weyl state in EuCd₂As₂ is still missing. Here, we successfully synthesized highly insulating crystals EuCd₂As₂ and were able to control the carrier density by several orders of magnitude. We observed colossal negative magnetoresistance in low carrier density EuCd₂As₂ when the external magnetic field polarized the spins. However, the anomalous Hall conductivity (AHC) decreases by several orders of magnitude as the carrier density decreases. This behavior is inconsistent with the AHC resulted from the Berry curvature generated by the Weyl points, which is independent of carrier density. Our electrical transport result suggests that more studies are required to elucidate the nature of the topological phase of FM EuCd₂As₂.