Magnetically tunable Dirac and Weyl fermions in the Zintl materials family

TL;DR

This paper explores how doping and external fields can induce various topological phases in the SrIn$_2$As$_2$ family, revealing a versatile platform for studying Weyl and Dirac fermions in topological materials.

Contribution

It demonstrates the tunability of topological states in SrIn$_2$As$_2$ family through doping and external fields, introducing a new platform for topological fermion research.

Findings

SrIn$_2$As$_2$ is a dual topological insulator with specific invariants.

EuIn$_2$As$_2$ is an axion insulator with distinct topological properties.

Magnetic field induces Weyl or nodal fermion states in EuIn$_2$P$_2$.

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.