Detection of magnetic gap in the topological surface states of MnBi2Te4

TL;DR

This study confirms the existence of a magnetic gap in MnBi2Te4's topological surface states using tunneling spectroscopy, linking it to surface ferromagnetism and temperature-dependent magnetic properties.

Contribution

It provides experimental evidence of the magnetic gap in MnBi2Te4's surface states and correlates it with ferromagnetism and temperature effects, advancing understanding of magnetic topological insulators.

Findings

Surface gap size is approximately 50 meV.

The gap vanishes with increasing temperature.

Magnetoresistance hysteresis confirms surface ferromagnetism.

Abstract

Recently, intrinsic antiferromagnetic topological insulator MnBi2Te4 has drawn intense research interest and leads to plenty of significant progress in physics and materials science by hosting quantum anomalous Hall effect, axion insulator state, and other quantum phases. An essential ingredient to realize these quantum states is the magnetic gap in the topological surface states induced by the out-of-plane ferromagnetism on the surface of MnBi2Te4. However, the experimental observations of the surface gap remain controversial. Here, we report the observation of the surface gap via the point contact tunneling spectroscopy. In agreement with theoretical calculations, the gap size is around 50 meV, which vanishes as the sample becomes paramagnetic with increasing temperature. The magnetoresistance hysteresis is detected through the point contact junction on the sample surface with an out-of-plane magnetic field, substantiating the surface ferromagnetism. Furthermore, the non-zero transport spin polarization coming from the ferromagnetism is determined by the point contact Andreev reflection spectroscopy. Combining these results, the magnetism-induced gap in topological surface states of MnBi2Te4 is revealed.