First-principles study of electronic structure, transport, and optical properties of EuCd2As2

Abstract

Recent experimental measurements on the layered triangular-lattice antiferromagnet ${\mathrm{EuCd}}_{2}{\mathrm{As}}_{2}$ have revealed an interesting interplay among magnetism, charge transport, and optical properties. To explore the nature of the interaction among these degrees of freedom, the electronic structure, magnetic properties, electrical transport, and optical properties of ${\mathrm{EuCd}}_{2}{\mathrm{As}}_{2}$ are investigated using density functional theory and Boltzmann transport theory under various approximations such as the generalized gradient approximation (GGA), GGA+$U$, and GGA+$U$+spin orbit (SO). A semimetallic electronic structure with compensating electron and hole pockets is observed. Among the various magnetic states studied, A-type antiferromagnetic (A-AFM) and ferromagnetic (FM) states emerge as having competing total energies even though A-AFM is found to be energetically favored. Further, our GGA+$U$+SO calculations reveal the presence of a magnetic anisotropy which drives the spin moments to align along the crystallographic $b$ direction. We observe from our transport calculations that in the case of A-AFM, the anisotropy between out-of-plane and in-plane resistivities $({\ensuremath{\rho}}_{zz}/{\ensuremath{\rho}}_{xx})$ is much higher than that in the FM case, and it increases as temperature goes down, exactly what has been observed experimentally for this system. The huge difference between the resistivities of A-AFM and FM states at lower temperatures is indicative of the presence of negative magnetoresistance in the system as seen in the experimental measurements. In-plane optical reflectivity reveals that intraband contributions play a major role in reproducing the experimental features in the low-frequency regime.