Visualizing the interplay of Dirac mass gap and magnetism at nanoscale in intrinsic magnetic topological insulators

TL;DR

This study visualizes and analyzes the Dirac mass gap in intrinsic magnetic topological insulators, revealing how magnetic defects influence the gap and providing insights for designing materials with exotic quantum states.

Contribution

It unambiguously identifies the Dirac mass gap in MnBi2Te4 and links its spatial variation to magnetic defects using experimental and theoretical methods.

Findings

Dirac mass gap visualized and measured directly.

Gap collapses in high defect regions.

Microscopic origin of gap variation explained by models.

Abstract

In intrinsic magnetic topological insulators, Dirac surface state gaps are prerequisites for quantum anomalous Hall and axion insulating states. Unambiguous experimental identification of these gaps has proved to be a challenge, however. Here we use molecular beam epitaxy to grow intrinsic MnBi2Te4 thin films. Using scanning tunneling microscopy/spectroscopy, we directly visualize the Dirac mass gap and its disappearance below and above the magnetic order temperature. We further reveal the interplay of Dirac mass gaps and local magnetic defects. We find that in high defect regions, the Dirac mass gap collapses. Ab initio and coupled Dirac cone model calculations provide insight into the microscopic origin of the correlation between defect density and spatial gap variations. This work provides unambiguous identification of the Dirac mass gap in MnBi2Te4, and by revealing the microscopic origin of its gap variation, establishes a material design principle for realizing exotic states in intrinsic magnetic topological insulators.