Observation of coherent ferron emission and propagation.

Coherent ferrons—polarization waves—are observed in van der Waals ferroelectrics NbOI2 and WO2Br2, producing intense narrow-band terahertz emission at the ferroelectric transverse optical phonon frequency.

• Why it matters: Ferroelectrics could host collective polarization modes analogous to magnons, but direct coherent evidence for their fundamental quanta, ferrons, has been lacking.
• What they did: The team used pulsed laser excitation of NbOI2 and WO2Br2 and tracked two signatures: narrow-band terahertz emission and uniaxial propagation as hyperbolic phonon polaritons.
• The result: The polarization waves propagate uniaxially along the polar axis with exceptionally long coherence times, enabling long-lived, dipole-carrying ferronic dynamics for narrow-band terahertz emission and coherent electric control.

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