  We have performed angle-resolved photoemission spectroscopy on EuIn2As2 which
is predicted to be an axion insulator in the antiferromagnetic state. By
utilizing soft-x-ray and vacuum-ultraviolet photons, we revealed a
three-dimensional hole pocket centered at the Gamma point of bulk Brillouin
zone together with a heavily hole-doped surface state in the paramagnetic
phase. Upon entering the antiferromagnetic phase, the band structure exhibits a
marked reconstruction characterized by the emergence of a "M"-shaped bulk band
near the Fermi level. The qualitative agreement with first-principles
band-structure calculations suggests the occurrence of bulk-band inversion at
the Gamma point in the antiferromagnetic phase. We suggest that EuIn2As2
provides a good opportunity to study the exotic quantum phases associated with
possible axion-insulator phase.
