Anisotropic magnetism and electronic structure of trigonal EuAl${}_2$Ge${}_2$ single crystals

Abstract

The magnetic and electronic properties of the layered Zintl-phase compound EuAl${}_2$Ge${}_2$ crystallizing in the trigonal CaAl${}_2$Si${}_2$-type structure are reported. Our neutron-diffraction measurements show that EuAl${}_2$Ge${}_2$ undergoes A-type antiferromagnetic (AFM) ordering below $T_{\mathrm{N}}=27.5(5)$~K, with the Eu moments (Eu${}^{2+}$, $S=7/2$) aligned ferromagnetically in the $ab$ plane. The $H=0$ magnetic structure consists of trigonal AFM domains associated with $ab$-plane magnetic anisotropy and a field-induced reorientation of the Eu spins in the domains is evident at $T=2$~K below the critical field $H_{c1}=2.5(1)$ kOe. Electrical resistivity and ARPES measurements show that EuAl${}_2$Ge${}_2$ is metallic both above and below $T_{\mathrm{N}}$. In the AFM phase, we directly observe folded bands in ARPES due to the doubling of the magnetic unit cell along the $c$ axis with an enhancement of quasiparticle weight due to the complex change in the coupling between the magnetic moments and itinerant electrons on cooling below $T_{\mathrm{N}}$. The observed electronic structure is well reproduced by first-principle calculations, which also predict the presence of nontrivial electronic states near the Fermi level in the AFM phase with $Z_2$ topological numbers 1;(000).

16 pages, 13 captioned figures, 53 references Updated several affiliations

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