Gapless Dirac surface states in the antiferromagnetic topological insulator <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>MnBi</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>Te</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:mrow></mml:math>

Abstract

A topological insulator can be converted to an axion insulator when time reversal symmetry is broken, which leads to the opening of a gap in the Dirac surface state. Recently, MnBi${}_{2}$Te${}_{4}$ was predicted to host such a state upon antiferromagnetic ordering. Collecting and analyzing very detailed photoemission data, the authors demonstrate that this does not occur and that the Dirac surface state remains gapless well below the N\'eel temperature. Most likely, this is due to the complexity of the magnetic ordering at the surface. The quest for the discovery of an axion insulator is, therefore, still on.

Topics & Concepts