Optics as a Probe and Control of Spin/Valley Order in Topological Moiré Magnet MoTe₂

In the past year, near-AA stacked homobilayer moiré MoTe₂ has been established as a robust, gate-tunable ferromagnet upon hole doping of the first moiré valence band. The system’s spontaneous time reversal symmetry breaking enables the realization of an effective Haldane model and flat, topologically nontrivial bands. These unique characteristics of the moiré MoTe₂ system led to observation of quantum anomalous Hall and, for the first time, fractional quantum anomalous Hall states. Here, I discuss our optical measurements of tunable magnetic and topological states in the moiré superlattice. Additionally, I present our more recent studies leveraging the magnetic order in the system to control helical optical emission at zero applied magnetic field. The strong correspondence between the spin, valley, and optical degrees of freedom these results establish suggests that optics is not only a powerful probe of moiré MoTe₂, but could also be promising control knob for the magnetic states. Beyond the implications for spintronics, valleytronics, and magneto-optical devices, the link between magnetic order and topological index of the FQAH states presents a new path forward in the study of anyon physics – and perhaps, one day, towards topological qubits.