Unraveling Magnetoelectric effect in Axion insulator candidate EuIn2As2

Topological materials have taken center stage of condensed matter physics. The Axion insulator is theoretically predicted as a novel class of topological materals, while experimental realization is lacking. EuIn2As2 has been proposed to be a promising candidate for the Axion insulator. In this work, we perform optical Second Harmonic Generation(SHG) and symmetry analysis to understand its magnetic order. We also surprisingly find the SHG anisotropy is sensitive to tiny external magnetic field. While breaking both P and T by the intrinsic magnetic order, it allows for magnetoelectric effect. Our work suggests exciting potential to use Axion insulators as functional magnetoelectric devices.