  The higher order topological insulator (HOTI) has enticed enormous research
interests owing to its novelty in supporting gapless states along the hinges of
the crystal. Despite several theoretical predictions, enough experimental
confirmation of HOTI state in crystalline solids is still lacking. It has been
well known that interplay between topology and magnetism can give rise to
various magnetic topological states including HOTI and Axion insulator states.
Here using the high-resolution angle-resolved photoemission spectroscopy
(ARPES) combined with the first-principles calculations, we report a systematic
study on the electronic band topology across the magnetic phase transition in
EuIn2As2 which possesses an antiferromagnetic ground state below 16 K.
Antiferromagnetic EuIn2As2 has been predicted to host both the Axion insulator
and HOTI phase. Our experimental results show the clear signature of the
evolution of the topological state across the magnetic transition. Our study
thus especially suited to understand the interaction of higher order topology
with magnetism in materials.
