Understanding transport and topology in EuCd₂X₂ through electronic structure: X = P vs. As

The symmetry breaking required to host a single pair of Weyl points seems to be realized in EuCd₂As₂, and importantly, can be tuned by energetically close magnetic ground states. Another tuning parameter is to change out the pnictogen for phosphorus instead of arsenic. The cousin compound, EuCd₂P₂ exhibits a surprisingly enormous collossal magneto-resistance (CMR), much larger than EuCd₂As₂ and even outperforming the traditional manganese oxides while not possessing any of the properties that explain their CMR. Therefore, this series of compounds provides a rich intersection where physics of strong correlation lie in close proximity to nontrivial topology. We systematically investigate the electronic structure of EuCd₂X₂ with X= {P, As} using both angle-resolved photo-emission spectroscopy (ARPES) and density functional theory (DFT). With remarkable agreement between experiment and theory, we provide a solid foundation to elucidate the rich transport behavior, spectroscopic signal related to magneto-resistance, and topological classification for these compounds.