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We use time-resolved nonlinear pump–probe measurements to reveal features of semiconductor moiré materials not accessible to linear spectroscopy. With an intense, red-detuned pump pulse, we generate a high density of virtual excitons or exciton–polarons in various moiré minibands. A broadband probe pulse in turn measures the response of all optical resonances induced by the pump-generated excitations. We generically observe a coherent blue shift originating from contact- like exciton–exciton interactions. At charge neutrality, these measurements allow us to assess the spatial overlap between different optical excitations and to observe signatures of a bound biexciton state between two different moiré exciton modes. In contrast to electron doped monolayers, spatially confined moiré attractive polarons behave as an ensemble of non-interacting two-level emitters, exhibiting an electron-density-independent ac-Stark effect. Tuning the pump laser into resonance with the attractive polaron, we demonstrate the filling of the moiré lattice with localized polarons and thereby realize a nonequilibrium Bose–Fermi mixture in moiré flat bands.

Rights:

• Creative Commons BY Attribution 4.0 International
  

Keyword: ac Stark spectroscopy, moiré excitons
, polarons


Date published: 2025-04-01

Publisher: American Physical Society (APS)

Journal:

• Physical Review X (ISSN: 21603308) vol. 15 issue. 2 021002

Funding:

• Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung 200020_207520

Manuscript type: Publisher's version (Version of record)

MDR DOI:

First published URL: https://doi.org/10.1103/physrevx.15.021002

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Updated at: 2026-02-16 16:30:31 +0900

Published on MDR: 2026-02-16 13:57:31 +0900