Energy gap of topological surface states in proximity to a magnetic insulator

TL;DR

This study measures the energy gap of topological surface states near a magnetic insulator, revealing weak magnetic proximity effects that influence potential spintronic applications and the realization of quantum anomalous Hall effect.

Contribution

The paper provides the first measurement of the energy gap in topological surface states adjacent to a magnetic insulator using magnetooptical Landau level spectroscopy.

Findings

The energy gap is likely due to quantum confinement effects.

Magnetic proximity effect is weak in the studied heterostructures.

Weak magnetic coupling favors spintronic device applications.

Abstract

Topological surface-states can acquire an energy gap when time-reversal symmetry is broken by interfacing with a magnetic insulator. This gap has yet to be measured. Such topological-magnetic insulator heterostructures can host a quantized anomalous Hall effect and can allow the control of the magnetic state of the insulator in a spintronic device. In this work, we observe the energy gap of topological surface-states in proximity to a magnetic insulator using magnetooptical Landau level spectroscopy. We measure Pb1-xSnxSe/EuSe heterostructures grown by molecular beam epitaxy exhibiting a record mobility and low Fermi energy. Through temperature dependent measurements and theoretical calculations, we show this gap is likely due to quantum confinement and conclude that the magnetic proximity effect is weak in this system. This weakness is disadvantageous for the realization of the quantum anomalous Hall effect, but favorable for spintronic devices which require the preservation of spin-momentum locking at the Fermi level.