Gapless Dirac surface states in the antiferromagnetic topological insulator MnBi2Te4

Understand

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.