Giant and Helical Exciton Dipole from Berry Curvature in Flat Chern Bands

We show that excitons forming between moiré flat Chern bands possess a substantial electric dipole moment comparable to the moiré lattice parameter times the elementary charge (∼10^{2}  D). At a hole filling factor of 1 in twisted MoTe_{2}, the dipole moment of the lowest-energy exciton branch develops in-plane helical texture in momentum space from the intrinsic Berry curvature of electron and hole. By solving the Bethe-Salpeter equations, we demonstrate that an out-of-plane displacement field induces a Frenkel-to-Wannier exciton transition, accompanied by a reversal of the dipole texture helicity. The giant dipole produces an attractive dipole-dipole interaction channel, suggesting a possible quadrupolar biexciton measurable via two-photon spectroscopy. Our findings establish band topology as a tunable knob to engineer exciton dipole moments and pave the way to manipulate many-body interactions in the terahertz regime.