Chiral edge mode for single-cone Dirac fermions

TL;DR

This paper investigates the emergence of a chiral edge mode on the surface of a 3D topological insulator interfaced with a magnetic insulator, revealing conditions for its existence and its properties, including its momentum space structure and charge pumping capabilities.

Contribution

It introduces a novel analysis of chiral edge modes on TI surfaces with magnetic insulators, detailing their dependence on magnetization angle and chemical potential mismatch, and characterizing their momentum space and charge transport features.

Findings

Chiral edge mode appears along TI-MI boundary depending on magnetization angle and chemical potential mismatch.

The edge mode propagates with velocity less than the Dirac fermion velocity, following a specific angular dependence.

Charge is pumped between TI and MI via the arc state when an electric field is applied parallel to the boundary.

Abstract

We study the appearance of a chiral edge mode on the two-dimensional (2D) surface of a 3D topological insulator (TI). The edge mode appears along the 1D boundary with a magnetic insulator (MI), dependent on the angle $\theta$ which the magnetization $M$ makes with the normal to surface and on the chemical potential mismatch $\delta\mu$ across the TI--MI interface (assuming $1>\delta\mu/M\equiv\sin\phi)$. The propagation along the interface is chiral, with velocity $v\cos(\theta-\phi)$ smaller than the Dirac fermion velocity $v$. In momentum space the edge mode is an arc state, extending over the finite momentum interval that connects the Dirac point of the gapless Dirac fermions with the magnetic band gap. An electric field parallel to the boundary pumps charge between TI and MI via this arc state.