Electronic and Topological Properties of a Topological Insulator Thin Film Sandwiched between Ferromagnetic Insulators

TL;DR

This paper investigates how a topological insulator thin film sandwiched between ferromagnetic insulators exhibits tunable electronic and topological properties, including transitions to quantum Hall states, influenced by magnetic configuration and gate voltage.

Contribution

It introduces a model analyzing the effects of magnetic proximity and external gating on the topological and transport properties of TI thin films.

Findings

Magnetization affects surface state transport properties.

Gate voltage can induce topological phase transitions.

System can reach anomalous quantum Hall state.

Abstract

We consider a thin film of a topological insulator (TI) sandwiched between two ferromagnetic (FM) layers. The system is additionally under an external gate voltage. The surface electron states of TI are magnetized due to the magnetic proximity effect to the ferromagnetic layers. The magnetization of ferromagnetic layers can be changed by applying an external magnetic field or by varying thickness of the topological insulator (owing to the interlayer exchange coupling). The change in the magnetic configuration of the system affects the transport properties of the surface electronic states. Using the Green function formalism, we calculate spin polarization, anomalous Hall effect, and magnetoresistance of the system. We show, among others, that by tuning the gate voltage and magnetizations of the top and bottom FM layers, one can observe the topological transition to the anomalous quantum Hall state.