Half-quantized anomalous Hall conductance in topological insulator/ferromagnet van der Waals heterostructures

TL;DR

This paper investigates the realization of half-quantized anomalous Hall conductance in topological insulator/ferromagnet heterostructures using first-principles and tight-binding models, highlighting experimental challenges.

Contribution

It provides a detailed theoretical analysis of magnetization-induced gaps and sidewall states in FI/TI heterostructures relevant for experiments.

Findings

Identified factors hindering exact half-quantization in realistic systems.

Analyzed the properties of sidewall states in heterostructures.

Discussed implications for quantum anomalous Hall and topological magnetoelectric effects.

Abstract

The half-quantized anomalous Hall conductance (AHC) in topological materials is a condensed matter physics realization of the parity anomaly of (2+1) quantum field theory and an important challenge for both theoretical and experimental research. A possible realization of this phenomenon may be achieved by interfacing a two-dimensional (2D) ferromagnetic (FM) layer with one surface of a thin slab of a topological insulator (TI), which breaks the otherwise conserved time-reversal symmetry, leading to a gap opening in the Dirac-like energy spectrum of the TI surface states. The resulting heterostructure can support chiral currents where only one spin channel contributes to transport, producing a half-quantized Hall conductance ($e^2/2h$). In this work, using first-principles methods together with tight-binding models, we investigate the magnetization-induced gap, the properties of the sidewalls states, and Hall conductance in three different FI/TI van der Waals heterostructures that are relevant for ongoing experiments. We also discuss the factors that can hinder the realization of exact half-quantization in a realistic system and their implication for the quantum anomalous Hall effect and the topological magnetoelectric effect.