Bonding Interactions Can Drive Topological Phase Transitions in a Zintl Antiferromagnetic Insulator

TL;DR

This study explores how chemical pressure via Ga substitution in Eu-based Zintl compounds can induce topological phase transitions, potentially leading to magnetic topological insulators by band inversion driven by Eu-Sb hybridization.

Contribution

It demonstrates the role of chemical pressure in driving topological phase transitions in Eu-based Zintl compounds, highlighting band inversion mechanisms and the potential for intrinsic magnetic topological insulators.

Findings

Eu$_5$Ga$_2$Sb$_6$ predicted to be topological

Eu$_{5}$In$_{4/3}$Ga$_{2/3}$Sb$_{6}$ synthesized and characterized

Band inversion linked to Eu-Sb hybridization changes

Abstract

While $\sim$30% of materials are reported to be topological, topological insulators are rare. Magnetic topological insulators (MTI) are even harder to find. Identifying crystallographic features that can host the coexistence of a topological insulating phase with magnetic order is vital for finding intrinsic MTI materials. Thus far, most materials that are investigated for the determination of an MTI are some combination of known topological insulators with a magnetic ion such as MnBi$_2$Te$_4$. Motivated by the recent success of EuIn$_{2}$As$_{2}$, we investigate the role of chemical pressure on topologically trivial insulator, Eu$_5$In$_2$Sb$_6$ via Ga substitution. Eu$_5$Ga$_2$Sb$_6$ is predicted to be topological but is synthetically difficult to stabilize. We look into the intermediate compositions between Eu$_5$In$_2$Sb$_6$ and Eu$_5$Ga$_2$Sb$_6$ through theoretical works to explore a topological phase transition and band inversion mechanism. We attribute the band inversion mechanism to changes in Eu-Sb hybridization as Ga is substituted for In due to chemical pressure. We also synthesize Eu$_{5}$In$_{4/3}$Ga$_{2/3}$Sb$_{6}$, the highest Ga concentration in Eu$_{5}$In$_{2-x}$Ga$_{x}$Sb$_{6}$, and report the thermodynamic, magnetic, transport, and Hall properties. Overall, our work paints a picture of a possible MTI via band engineering and explains why Eu-based Zintl compounds are suitable for the co-existence of magnetism and topology.