Helical Light Emission from a Moiré Chern Magnet

Twisted MoTe₂ bilayer is an emergent fractional Chern insulator with spontaneous time reversal breaking. As semiconducting transition metal dichalcogenides famously exhibit spin-valley locking and circularly polarized valley-optical selection rules, a natural question arises as to how the interaction induced ferromagnetism couples to the optical response. Here, we demonstrate that the degree of circular polarization (DOCP) in the trion photoluminescence at zero magnetic field reaches near unity in the anomalous Hall metal phase, with the helicity controlled by the magnetization direction. Spin-valley Hall response is shown to tune the emission helicity, establishing the electric current as an additional control of the PL helicity. We further show that the PL DOCP is a sensitive probe of the integer and fractional quantum anomalous Hall effects, the putative zero-field composite fermi liquid state, as well as their electric field-driven topological quantum phase transitions. The unprecedented optical properties of this system promise to have profound implications for spintronics, valleytronics, and topological-optoelectronic devices.