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arXiv · 2604.12295

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

Kaijie Yang·Huiyuan Zheng·Xiaodong Xu·Di Xiao·Ting Cao
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Abstract

We show that excitons forming between moir\'e flat Chern bands possess a substantial electric dipole moment comparable to the moir\'e lattice parameter times the elementary charge ($\sim10^2$ Debye). At a hole filling factor of one 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 resulting attractive exciton dipole-dipole interactions lead to quadrupolar biexcitons that can be probed 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.

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Kaijie Yang, Huiyuan Zheng, Xiaodong Xu, Di Xiao, Ting Cao. 2026-04-14. Giant and Helical Exciton Dipole from Berry Curvature in Flat Chern Bands. https://arxiv.org/abs/2604.12295

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