# Gapless Dirac surface states in the antiferromagnetic topological insulator MnBi2Te4

## TL;DR

This study combines ARPES and DFT to reveal that MnBi2Te4 hosts gapless Dirac surface states that are robust across its antiferromagnetic transition, challenging previous assumptions of a gapped surface state in such materials.

## Contribution

The paper provides the first experimental evidence of gapless Dirac surface states in an intrinsic antiferromagnetic topological insulator, MnBi2Te4, across its magnetic transition.

## Key findings

- Gapless Dirac cone remains protected across the AFM transition.
- A second Dirac cone exists near the Fermi level as predicted.
- Bulk band splitting occurs below the Néel temperature.

## Abstract

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.