Electric field modulated topological magnetoelectric effect in Bi$_2$Se$_3$

TL;DR

This paper demonstrates an ionic gel gating technique to tune the chemical potential of Bi$_2$Se$_3$ thin films, enabling the observation of a quantized topological magnetoelectric effect via THz spectroscopy.

Contribution

It introduces a novel ionic gel gating method to control the Fermi level in topological insulator films, facilitating the experimental detection of topological magnetoelectric phenomena.

Findings

Carrier concentration can be tuned by an order of magnitude.

Fermi energy can be shifted close to the Dirac point.

Quantized Faraday angle observed, consistent with topological magnetoelectric effect.

Abstract

Topological insulators have been predicted to exhibit a variety of interesting phenomena including a quantized magnetoelectric response and novel spintronics effects due to spin textures on their surfaces. However, experimental observation of these phenomena has proved difficult due to the finite bulk carrier density which may overwhelm the intrinsic topological responses that are expressed at the surface. Here, we demonstrate a novel ionic gel gating technique to tune the chemical potential of Bi$_{2}$Se$_{3}$ thin films while simultaneously performing THz spectroscopy. We can tune the carrier concentration by an order of magnitude and shift the Fermi energy, E$_{F} $ to as low as $\simeq$ 10 meV above the Dirac point. At high bias voltage and magnetic field, we observe a quantized Faraday angle consistent with the topological magnetoelectric effect that can be tuned by ionic gel gating through a number of plateau states