Tunable nonlinear polaritons in moiré and strongly correlated materials

by Prof. Kok Wee Song (Deaprtment of Physics, Xiamen University Malaysia)

Tuesday 22 Sept 2026, 14:20 → 15:20 Asia/Taipei

Physics/019 (NTHU)

Two-dimensional semiconductors and magnetic van der Waals materials offer a uniquely tunable platform for engineering strong light-matter coupling, where moiré superlattices and strong electronic correlations combine to produce rich, controllable optical nonlinearities. In this talk, I will present a microscopic theory of moiré exciton-polaritons in twisted transition metal dichalcogenide (TMD) bilayers, showing how the interplay of interlayer tunneling, twist angle, and applied electric field enables electrically tunable and enhanced polariton nonlinearity, including a crossover between attractive and repulsive interaction regimes. I will then discuss how nonlinear phase-space filling and Pauli blocking govern polariton saturation in lattice and doped systems, connecting this framework to a recent charge-tunable experiment on a gate-controllable MoTe₂-MoSe₂ heterobilayer cavity. Extending beyond excitons, I will show how Coulomb scattering between trions gives rise to an unusually strong attractive polariton nonlinearity, offering a distinct route to interacting photonic fluids. Finally, I will turn to strongly correlated van der Waals magnets, presenting a microscopic superexchange theory for chromium trihalides and recent results on exciton-polariton condensation in the magnetic semiconductor CrSBr, highlighting the emerging opportunities at the intersection of magnetism, strong correlations, and cavity photonics.