Coupling of electronic transition to ferroelectric order in a 2D semiconductor.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 39988629.
- Also identified by DOI 10.1038/s41467-025-57061-9 and PMC identifier 11847933.
- Licence recorded as CC BY-NC-ND.
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Abstract
A ferroelectric material often exhibits a soft transverse optical (TO) phonon mode which governs its phase transition. Charge coupling to this ferroelectric soft mode may further mediate emergent physical properties, including superconductivity and defect tolerance in semiconductors. However, direct experimental evidence for such coupling is scarce. Here we show that a photogenerated coherent phonon couples strongly to the electronic transition above the bandgap in the van der Waals (vdW) two-dimensional (2D) ferroelectric semiconductor NbOI<sub>2</sub>. Using terahertz time-domain spectroscopy and first-principles calculations, we identify this mode as the TO phonon responsible for ferroelectric order. This exclusive coupling occurs only with the above-gap electronic transition and is absent in the valence band as revealed by resonant inelastic X-ray scattering. Our findings suggest a new role of the soft TO phonon mode in electronic and optical properties of ferroelectric semiconductors.