Electrical Probing of Dark Excitons through Microwave Permittivity

Abstract

Excitons in atomically thin semiconductors are almost always probed through their optical signatures, because the short lifetimes of these transient quasiparticles are generally assumed to preclude electrical detection. Here we show that photoexcited excitons in monolayer tungsten disulfide produce a large, optically tunable permittivity at gigahertz frequencies, and that the effect provides a contact-free electrical route to imaging dark excitons at the nanoscale. Using laser-illuminated microwave impedance microscopy, we find that high-purity encapsulated flakes exhibit a purely dielectric response resonant with the exciton spectrum, whereas defect-rich samples are governed by conventional photoconductivity. Spatial mapping of diffusion and sublinear power dependence identify long-lived dark excitons as the dominant contributors, and first-principles modelling of exciton polarizability reproduces the measured susceptibility. Our results establish excitons as optically tunable dielectric elements and introduce microwave microscopy as a direct electrical probe of dark-exciton transport with sub-100 nm resolution.

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BibTeX RIS

BibTeX

@misc{stram2026electrical,
  title = {{Electrical Probing of Dark Excitons through Microwave Permittivity}},
  author = {Alex Stram and Zhida Liu and Ziheng Zhang and Yangchen He and Xuejian Ma and Kyoung Pyo Lee and Lisa Frammolino and Fuxiang Chen and Robert J. Boyd and Sirapas Tangton and Anand Swain and Kan Yao and Kenji Watanabe and Takashi Taniguchi and Yuebing Zheng and Chih-Kang Shih and Daniel Rhodes and Li Yang and Xiaoqin Li and Keji Lai},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.22710},
  eprint = {2609.22710},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.22710},
}

RIS

TY  - UNPB
TI  - Electrical Probing of Dark Excitons through Microwave Permittivity
AU  - Alex Stram
AU  - Zhida Liu
AU  - Ziheng Zhang
AU  - Yangchen He
AU  - Xuejian Ma
AU  - Kyoung Pyo Lee
AU  - Lisa Frammolino
AU  - Fuxiang Chen
AU  - Robert J. Boyd
AU  - Sirapas Tangton
AU  - Anand Swain
AU  - Kan Yao
AU  - Kenji Watanabe
AU  - Takashi Taniguchi
AU  - Yuebing Zheng
AU  - Chih-Kang Shih
AU  - Daniel Rhodes
AU  - Li Yang
AU  - Xiaoqin Li
AU  - Keji Lai
PY  - 2026
DA  - 2026/09/19
PB  - arXiv
DO  - 10.48550/arxiv.2609.22710
UR  - https://arxiv.org/abs/2609.22710
AB  - Excitons in atomically thin semiconductors are almost always probed through their optical signatures, because the short lifetimes of these transient quasiparticles are generally assumed to preclude electrical detection. Here we show that photoexcited excitons in monolayer tungsten disulfide produce a large, optically tunable permittivity at gigahertz frequencies, and that the effect provides a contact-free electrical route to imaging dark excitons at the nanoscale. Using laser-illuminated microwave impedance microscopy, we find that high-purity encapsulated flakes exhibit a purely dielectric response resonant with the exciton spectrum, whereas defect-rich samples are governed by conventional photoconductivity. Spatial mapping of diffusion and sublinear power dependence identify long-lived dark excitons as the dominant contributors, and first-principles modelling of exciton polarizability reproduces the measured susceptibility. Our results establish excitons as optically tunable dielectric elements and introduce microwave microscopy as a direct electrical probe of dark-exciton transport with sub-100 nm resolution.
ER  -

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