Magnetically tunable Dirac and Weyl fermions in the Zintl materials family

Abstract

Recent classification efforts encompassing crystalline symmetries have revealed rich possibilities for solid-state systems to support a tapestry of exotic topological states. However, finding materials that realize such states remains a daunting challenge. Here we show how the interplay of topology, symmetry, and magnetism combined with doping and external electric and magnetic field controls can be used to drive the previously unreported SrIn${}_2$As${}_2$ materials family into a variety of topological phases. Our first-principles calculations and symmetry analysis reveal that SrIn${}_2$As${}_2$ is a dual topological insulator with $Z_2=(1;000)$ and mirror Chern number $C_M=-1$. Its isostructural and isovalent antiferromagnetic cousin EuIn${}_2$As${}_2$ is found to be an axion insulator with $Z_4=2$. The broken time-reversal symmetry via Eu doping in Sr${}_{1-x}$Eu${}_x$In${}_2$As${}_2$ results in a higher-order or topological crystalline insulator state depending on the orientation of the magnetic easy axis. We also find that antiferromagnetic EuIn${}_2$P${}_2$ is a trivial insulator with $Z_4=0$, and that it undergoes a magnetic field-driven transition to an ideal Weyl fermion or nodal fermion state with $Z_4=1$ with applied magnetic field. Our study identifies Sr${}_{1-x}$Eu${}_x$In${}_2$(As, P)${}_2$ as a new tunable materials platform for investigating the physics and applications of Weyl and nodal fermions in the scaffolding of crystalline and axion insulator states.

8 Pages, 4 Figures, SM not included

References in corpus (8)

• Topological Crystalline Insulators
• Antiferromagnetic topological insulators
• Discovery of topological Weyl fermion lines and drumhead surface states in a room temperature magnet
• Higher-order Topology of Axion Insulator EuIn${}_2$As${}_2$
• Magnetic crystalline-symmetry-protected axion electrodynamics and field-tunable unpinned Dirac cones in EuIn2As2
• Spin-orbit quantum impurity and quantization in a topological magnet
• Topological crystalline insulator state with type-II Dirac fermions in transition metal dipnictides
• Topological Descendants of Multicritical EuTl2