Magnetoelectric Control of Helical Light Emission in a Moiré Chern Magnet

Magnetoelectric effects and their coupling to light helicity are important for both fundamental science and applications in sensing, communication, and data storage. Traditional approaches require complex device architectures, involving separate spin-injection, ferromagnetic, and optically active layers. Recently, the emergence of 2D semiconductor moiré superlattices with flat Chern bands and strong light-matter interactions has established a simple yet powerful platform for exploring the coupling between photon, electron, and spin degrees of freedom. Here, we report efficient current control of spontaneous ferromagnetism and associated helicity of light emission in moiré <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:msub><a:mi>MoTe</a:mi><a:mn>2</a:mn></a:msub></a:mrow></a:math> bilayer—a system which hosts a rich variety of topological phases, including newly discovered zero-field fractional Chern insulators. We show that the current control is effective over a wide range of doping of the first moiré Chern band, implying the uniformity of the Berry curvature distribution over the flat band. By setting the system into the anomalous Hall metal phase, a current as small as 10 nA is sufficient to switch the magnetic order, a substantial improvement over both conventional spin-torque architectures and other moiré systems. The realized current control of ferromagnetism leads to continuous tuning of trion photoluminescence helicity from left to right circular via spin-valley Hall torque at zero magnetic field. Our results pave the way for topological optospintronics based on semiconductors with synthetic flat Chern bands.