Optical control over topological Chern number in moire materials

Understanding and controlling strongly correlated many-body spin systems is one of the key challenges in modern condensed matter physics. Among the most promising experimental platforms for these explorations are semiconducting moire materials (SMMs), which consist of two twisted or lattice-mismatched transition metal dichalcogenide monolayers. Owing to their spin-valley-selective optical selection rules and the possibility of incorporating them into charge-tunable devices, SMMs uniquely enable direct optical access to the spin degree of freedom of correlated electrons, whose density can be controlled in-situ using transparent graphene gates.



In this talk, I will describe our recent ultra-low-temperature magneto-optical investigations of collective electronic magnetism in twisted MoTe₂ homobilayers, where strong interlayer hybridization of hole orbitals gives rise to flat topological valence bands that support robust ferromagnetic metals as well as fractional and integer Chern insulators at various moire lattice filling factors. I will show that the spin state of all these topological ferromagnets can be dynamically reversed by resonantly driving exciton-polaron resonances in the optical absorption spectrum with circularly polarized light. This includes both integer and fractional Chern insulating phases, for which such a spin orientation is equivalent to all-optical switching of their many-body Chern number. Our spatially-resolved experiments demonstrate that by illuminating the sample with diffraction-limited spot, it is possible to induce such a Chern number flip in selected sample area, which paves the way for optical generation of programmable topological circuits.