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arXiv · 2505.06984

Excitons in fractionally-filled moiré superlattices

Junghwan Kim·Hanan Dery·Dinh Van Tuan
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Abstract

Long-range Coulomb forces give rise to correlated insulating states when charge particles populate a moiré superlattice at certain fractional filling factors. Such behavior is characterized by a broken translation symmetry wherein particles spontaneously form a Wigner crystal. Focusing on the experimental findings of Xu et al. [Nature \textbf{587}, 214 (2020)], we present a theory that captures the correlated insulating state of a fractionally-filled moiré superlattice through the energy shift and change in oscillator strength of the exciton absorption resonance. The theory shows that the experimental findings can only be supported if the electrons reside in a charge-ordered state (i.e., electrons are not randomly distributed among the sites of the moiré superlattice). Furthermore, we explain why the energy shifts of exciton resonances are qualitatively different in cases that the superlattice is nearly empty compared with a superlattice whose sites are doubly occupied.

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Junghwan Kim, Hanan Dery, Dinh Van Tuan. 2025-05-11. Excitons in fractionally-filled moiré superlattices. https://arxiv.org/abs/2505.06984

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