Intrinsic axion insulating behavior in antiferromagnetic <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>MnBi</mml:mi><mml:mn>6</mml:mn></mml:msub><mml:msub><mml:mi>Te</mml:mi><mml:mn>10</mml:mn></mml:msub></mml:mrow></mml:math>
Na Hyun Jo, Lin‐Lin Wang, Robert-Jan Slager, Jiaqiang Yan, Yun Wu, Kyungchan Lee, Benjamin Schrunk, Ashvin Vishwanath, Adam Kaminski
Abstract
A striking feature of time-reversal symmetry (TRS) protected topological insulators (TIs) is that they are characterized by a half integer quantum Hall effect on the boundary when the surface states are gapped by time-reversal breaking perturbations. While TRS-protected TIs have become increasingly under control, magnetic analogs are still a largely unexplored territory with novel rich structures. In particular, magnetic topological insulators can also host a quantized axion term in the presence of lattice symmetries. Since these symmetries are naturally broken on the boundary, the surface states can develop a gap without external manipulation. In this paper, we combine theoretical analysis, density-functional calculations and experimental evidence to reveal intrinsic axion insulating behavior in ${\mathrm{MnBi}}_{6}{\mathrm{Te}}_{10}$. The quantized axion term arises from the simplest possible mechanism in the antiferromagnetic regime where it is protected by inversion symmetry and the product of a fractional translation and TRS. The anticipated gapping of the Dirac surface state at the edge is subsequently experimentally established using angle resolved photoemission spectroscopy (ARPES). As a result, this system provides the magnetic analog of the simplest TRS-protected TI with a single, gapped Dirac cone at the surface.