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

Kaijie Yang1, Huiyuan Zheng1, Xiaodong Xu2,1, Di Xiao1,2, and Ting Cao1

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Phys. Rev. Lett. 137, 126602 – Published 15 September, 2026

DOI: https://doi.org/10.1103/5w7l-8mcv

Abstract

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 (∼102  D). At a hole filling factor of 1 in twisted MoTe2, 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.

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Phys. Rev. Lett. 137, 126602– Published 15 September, 2026
  • Received 14 April 2026
  • Accepted 10 August 2026
Article part of CHORUS
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