Topotaxial Mutual-Exchange Growth of Magnetic Zintl Eu$_3$In$_2$As$_4$ Nanowires with Axion Insulator Classification

TL;DR

This paper demonstrates a novel topotaxial mutual-exchange growth method to synthesize Eu$_3$In$_2$As$_4$ nanowires from InAs, revealing their magnetic and topological properties, including axion insulator classification and potential for advanced nanomaterial applications.

Contribution

It introduces a new solid-state topotactic exchange technique for converting InAs nanowires into Eu$_3$In$_2$As$_4$ nanowires, enabling exploration of magneto-topological states.

Findings

Eu$_3$In$_2$As$_4$ nanowires exhibit antiferromagnetic transition at ~6.5 K.

Ab initio calculations classify Eu$_3$In$_2$As$_4$ as a $C_2 T$ axion insulator.

The growth method allows synthesis of nanowires with exotic magnetic and topological properties.

Abstract

Nanomaterials bring to expression unique electronic properties that promote advanced functionality and technologies. Albeit, nanoscale growth presents paramount challenges for synthesis limiting the diversity in structures and compositions. Here, we demonstrate solid-state topotactic exchange that converts Wurtzite InAs nanowires into Zintl phase Eu$_3$In$_2$As$_4$ nanowires. In situ evaporation of Eu and As over InAs nanowire cores in molecular beam epitaxy results in mutual exchange of Eu from the shell and In from the core. A continuous Eu$_3$In$_2$As$_4$ shell thereby grows that gradually consumes the InAs core and converts it into a single phase Eu$_3$In$_2$As$_4$ nanowire. Topotaxy, which facilitates the mutual exchange, is supported by the substructure of the As matrix which is similar across the Wurtzite InAs and Zintl Eu$_3$In$_2$As$_4$. We provide initial evidence of an antiferromagnetic transition at T$_N$ $\sim$ 6.5 K in the Zintl phase Eu$_3$In$_2$As$_4$ nanowires. Ab initio calculation confirms the antiferromagnetic state and classifies Eu$_3$In$_2$As$_4$ as a $C_2 T$ axion insulator hosting both chiral hinge modes and unpinned Dirac surface states. The topotactic mutual-exchange growth of Zintl Eu$_3$In$_2$As$_4$ nanowires thus enables the exploration of intricate magneto-topological states of nanomaterials. Moreover, it may open the path for topotactic mutual-exchange synthesis of nanowires made of other exotic compounds.