Half-Magnetic Topological Insulator

TL;DR

This paper reports the discovery of a new half-magnetic topological insulator, MnBi8Te13, exhibiting a temperature-dependent surface gap and potential for axion electrodynamics, advancing understanding of magnetic topological materials.

Contribution

It introduces MnBi8Te13 as the first half-magnetic topological insulator with experimental evidence of a magnetization-induced surface gap and theoretical insights into its applications.

Findings

Massive Dirac gap (~28 meV) at MnBi2Te4 surface

Gap closes at Curie temperature, confirming magnetic origin

Potential to realize half-quantized anomalous Hall effect

Abstract

Topological magnets are a new family of quantum materials providing great potential to realize emergent phenomena, such as quantum anomalous Hall effect and axion-insulator state. Here we present our discovery that stoichiometric ferromagnet MnBi8Te13 with natural heterostructure MnBi2Te4-(Bi2Te3)3 is an unprecedented half-magnetic topological insulator, with the magnetization existing at the MnBi2Te4 surface but not at the opposite surface terminated by triple Bi2Te3 layers. Our angle-resolved photoemission spectroscopy measurements unveil a massive Dirac gap at the MnBi2Te4 surface, and gapless Dirac cone on the other side. Remarkably, the Dirac gap (~28 meV) at MnBi2Te4 surface decreases monotonically with increasing temperature and closes right at the Curie temperature, thereby representing the first smoking-gun spectroscopic evidence of magnetization-induced topological surface gap among all known magnetic topological materials. We further demonstrate theoretically that the half-magnetic topological insulator is desirable to realize the half-quantized surface anomalous Hall effect, which serves as a direct proof of the general concept of axion electrodynamics in condensed matter systems.