Researchers from the University of Konstanz, Institute of Science Tokyo and TU Dortmund University recently demonstrated that coherent terahertz (THz) magnons can transfer their coherence to electronic charges in the insulating antiferromagnet NiO, providing a crucial step toward energy‑efficient, THz‑speed spintronic devices compatible with CMOS technology. The core idea is that optically driven THz spin waves imprint a coherent, charge‑dominated signal onto the material’s optical response, realizing a spin‑to‑charge conversion stage mediated by light.
Collective spin excitations - magnons, i.e., quantized spin waves of large spin ensembles - naturally operate in the THz range and promise low‑loss information transfer, but integrating them with conventional electronics requires converting their spin signal into an electrical one. In this work, the team uses NiO as a prototypical dielectric antiferromagnet and excites coherent THz magnons with femtosecond laser pulses whose photon energy lies below the 4 eV bandgap, so that the primary excitation channel addresses the spin system rather than creating a dense electron–hole plasma.
The experiment is performed on a 50 µm‑thick NiO single crystal at cryogenic temperatures around 10 K, using visible-near‑infrared probe light (roughly 400-900 nm) to track the transient transmissivity ΔT/T on femtosecond-picosecond timescales. The resulting time traces show clear oscillations at about 1 THz, consistent with a magnon mode, and these oscillations appear only at photon energies where the static transmissivity spectrum has a significant slope, indicating that the THz spin dynamics modulate the energies of specific electronic transitions.
To explain this behavior, the authors develop a microscopic model for NiO that calculates the energies of the relevant d-d transitions and how they shift when the effective magnetic mean field is tilted by the optically driven magnons. The model predicts a spin-orbit-mediated, time‑dependent modulation of several electronic transitions, which in turn generates an oscillatory ΔT/T signal at the magnon frequency; the calculated spectra agree with experiment without any fine‑tuning of parameters.
In practical terms, this establishes an optically readable, coherent transduction path from THz magnons to an electronic (charge‑dominated) optical signal in a standard antiferromagnetic insulator. Such a mechanism can form the first stage of a spin‑to‑charge conversion chain, enabling hybrid magnonic–photonic–electronic links that combine the low‑loss, THz‑bandwidth advantages of magnons with established optoelectronic and CMOS technologies.