Influence of magnetic disorders on Quantum Anomalous Hall Effect in Magnetic Topological Insulator Films beyond the two-dimensional limit

TL;DR

This study investigates how magnetic disorders affect the Quantum Anomalous Hall Effect in three-dimensional magnetic topological insulator films, revealing that certain magnetic disorder configurations can protect and enhance QAHE.

Contribution

It provides the first numerical analysis of magnetic disorder effects on QAHE in 3D MTI films, highlighting the role of side surface states and film thickness.

Findings

QAHE is protected by gapless side surface states despite magnetic disorders.

Magnetic disorders can suppress dissipation and improve QAHE quality.

Optimal effects of magnetic disorders depend on film thickness.

Abstract

Quantum anomalous Hall effect (QAHE) has been experimentally realized in magnetic topological insulator (MTI) thin films fabricated on magnetically doped (Bi,Sb)2Te3. In a MTI thin film with the magnetic easy axis along the normal direction (z-direction), orientations of magnetic dopants are randomly distributed around the magnetic easy axis, acting as magnetic disorders. With the aid of the non-equilibrium Green's function and Landauer-Buttiker formalism, we numerically study the influence of magnetic disorders on QAHE in a MTI thin film modeled by a three-dimensional tight-binding Hamiltonian. It is found that, due to the existence of gapless side surface states, QAHE is protected even in the presence of magnetic disorders as long as the z-component of magnetic moment of all magnetic dopants are positive. More importantly, such magnetic disorders also suppress the dissipation of the chiral edge states and enhance the quality of QAHE in MTI films. In addition, the effect of magnetic disorders depends very much on the film thickness, and the optimal influence is achieved at certain thickness. These findings are new features for QAHE in three-dimensional systems, not present in two-dimensional systems.