Magnetoelectric effect in topological insulator films beyond the linear response regime

TL;DR

This paper investigates the magnetoelectric response of topological insulator films under strong fields beyond linear theory, revealing quantized effects and surface hybridization impacts through numerical modeling.

Contribution

It introduces a numerical approach to study nonlinear magnetoelectric effects in topological insulators, highlighting quantized plateaus and surface hybridization effects.

Findings

Quantized magnetoelectric polarizability observed.

Surface wave function hybridization reduces effect in thin films.

Multiple quantized $ heta$ plateaus linked to Landau levels.

Abstract

We study the response of topological insulator films to strong magnetic and electric fields beyond the linear response theory. As a model, we use the three-dimensional lattice Wilson-Dirac Hamiltonian where we simultaneously introduce both magnetic field through the Peierls substitution and electric field as a potential energy depending on lattice coordinate. We compute the electron energy spectrum by numerically diagonalizing this Hamiltonian and obtain quantized magnetoelectric polarizability. In addition, we find that the magnetoelectric effect vanishes as the film width decreases due to the hybridization of surface wave functions. Furthermore, applying a gate voltage between the surfaces, we observe several quantized plateaus of $\theta$ term, which are mainly determined by the Landau level structures on the top and bottom surfaces.