Coupling of magnetic order and charge transport in the candidate Dirac semimetal EuCd2As2

Abstract

We use resonant elastic x-ray scattering to determine the evolution of magnetic order in EuCd2As2 below TN = 9.5 K, as a function of temperature and applied magnetic field. We find an A-type antiferromagneticstructure with in-plane magnetic moments, and observe dramatic magnetoresistive effects associated with field-induced changes in the magnetic structure and domain populations. Our ab initio electronic structure calculations indicate that the Dirac dispersion found in the nonmagnetic Dirac semimetal Cd3As2 is also present in EuCd2As2, but is gapped for T < TN due to the breaking of C3 symmetry by the magnetic structure.

Ideal Weyl semimetal induced by magnetic exchange

“…Bulk single crystals of EuCd 2 As 2 (ECA) were grown by a NaCl/KCl flux method [17]. The magnetic, transport and crystallographic properties of the crystals were fully consistent with earlier reports [15][16][17] line of the beamline I05 at the Diamond Light Source, UK [19]. A Scienta R4000 analyzer was used to select a photon energy of 130 eV, which approximately corresponds to the k z = 0 measurement plane.…”

“…Below T N = 9.5 K the spins order in an A-type antiferromagnetic (AFM) structure in which the spins form ferromagnetic layers which stack antiferromagnetically along the c axis [ Fig. 2(a)] [15]. A relatively small magnetic field (B c = 1.6 T at T = 2 K for B c) can be used to coerce the Eu spins into a fully aligned state [15].…”

“…ECA is metallic at temperatures down to T ∼ 80 K, but for lower temperatures the resistivity increases to a sharp maximum at T N before falling again at lower temperatures. This behaviour has been interpreted as due to scattering of conduction electrons by fluctuations of localized Eu magnetic moments which are exchange-coupled to the Cd and As orbitals [15,16]. In previous ab initio electronic structure calculations, where spins in the AFM state were found to be aligned with the c axis, ECA was predicted to host a band inversion of doubly-degenerate As 4p and Cd 5s states near the Fermi level (E F ), producing a crossing along the Γ−A line protected by C 3 symmetry [15,24].…”

Emergence of Nontrivial Low‐Energy Dirac Fermions in Antiferromagnetic EuCd2As2

“…This indicates that the ordered moments are along the c ‐axis 23,24,28–30. On the other hand, a recent resonant elastic X‐ray scattering (REXS) study suggests the same A‐type antiferromagnetic structure, but with in‐plane ( ab ‐plane) magnetic moments 22…”

“…So far, two different A‐type AFM orders have been suggested for the magnetic ground state of EuCd 2 As 2 ,22–24 i.e., one with spin along the in‐plane direction22 and one with spin along the out‐of‐plane direction 23,24. Using density functional theory (DFT) calculations, we show that the DSM state can exist when the ground state of EuCd 2 As 2 is in the out‐of‐plane spin configuration.…”