Magnetic proximity effect in the 3D topological insulator/ferromagnetic insulator heterostructure

TL;DR

This paper theoretically investigates how the magnetic proximity effect influences the Dirac helical state in 3D topological insulator/ferromagnetic insulator heterostructures, predicting interface spin polarization and gap opening at the Dirac point.

Contribution

It introduces a theoretical model predicting spin polarization and energy gap formation at the TI/FMI interface due to magnetic proximity effects.

Findings

Spin polarization of interface states due to orbital mixing.

Induced exchange field creates a gap at the Dirac point.

Dependence of the gap size on material parameters estimated.

Abstract

We theoretically study the magnetic proximity effect in the three dimensional (3D) topological insulator/ferromagnetic insulator (TI/FMI) structures in the context of possibility to manage the Dirac helical state in TI. Within continual approach based on the $\mathbf{kp}$ Hamiltonian we predict that, when 3D TI is brought into contact with 3D FMI, the ordinary bound state arising at the TI/FMI interface becomes spin polarized due to the orbital mixing at the boundary. Whereas the wave function of FMI decays into the TI bulk on the atomic scale, the induced exchange field, which is proportional to the FMI magnetization, builds up at the scale of the penetration depth of the ordinary interface state. Such the exchange field opens the gap at the Dirac point in the energy spectrum of the topological bound state existing on the TI side of the interface. We estimate the dependence of the gap size on the material parameters of the TI/FMI contact.