  We use high-resolution, tunable angle-resolved photoemission spectroscopy
(ARPES) and density functional theory (DFT) calculations to study the
electronic properties of single crystals of MnBi2Te4, a material that was
predicted to be the first intrinsic antiferromagnetic (AFM) topological
insulator. We observe both bulk and surface bands in the electronic spectra, in
reasonable agreement with the DFT calculations results. In striking contrast to
the earlier literatures showing a full gap opening between two surface band
manifolds along (0001) direction, we observed a gapless Dirac cone remain
protected in MnBi2Te4 across the AFM transition (TN = 24 K). Our data also
reveal the existence of a second Dirac cone closer to the Fermi level,
predicted by band structure calculations. Whereas the surface Dirac cones seem
to be remarkably insensitive to the AFM ordering, we do observe splitting of
the bulk band that develops below the TN . Having a moderately high ordering
temperature, MnBi2Te4 provides a unique platform for studying the interplay
between topology and magnetic ordering.
