Surface state evolution induced by magnetic order in axion insulator candidate EuIn2As2

TL;DR

This study investigates how magnetic order affects the surface electronic states in EuIn2As2, an axion insulator candidate, revealing temperature-dependent partial gapping of topological surface states through combined experimental and theoretical approaches.

Contribution

It provides the first detailed experimental observation of surface state evolution in EuIn2As2, linking magnetic order to surface state gapping in an intrinsic magnetic topological insulator.

Findings

Partial gapping of surface states below AFM transition temperature.

Surface states persist with finite gap above the Néel temperature.

The bulk gap is approximately 120 meV, with surface state gapping around 40 meV.

Abstract

Gapping of Dirac surface states through time reversal symmetry breaking may realize the axion insulator state in condensed matter. Despite tremendous efforts, only a few material systems fall in this category of intrinsic magnetic topological insulators (TI). Recent theoretical calculations proposed the antiferromagnetic EuIn$_2$As$_2$ to be a topologically non-trivial magnetic insulator with gapped surface states. Here we use scanning tunneling microscopy and spectroscopy (STM/STS) complemented with density-functional theory (DFT) calculations and modelling to probe the surface electronic states in EuIn$_2$As$_2$. We find a spin-orbit induced bulk gap of ~120 meV located only a few meV above the Fermi energy, within which topological surface states reside. Temperature dependent measurements provide evidence of the partial gapping (~40 meV) of the surface states at low temperatures below the AFM order, which decreases with increasing temperature but remains finite above $T_N$