Photoengineering the Magnon Spectrum in an Insulating Antiferromagnet

TL;DR

This study demonstrates that ultrafast optical pulses can significantly alter the magnon spectrum in an insulating antiferromagnet, enabling dynamic control of spin dynamics for advanced magnonic applications.

Contribution

It reveals that resonant above-bandgap optical excitation in DyFeO3 can nearly collapse the magnon gap by transiently reducing the exchange interaction by 90%.

Findings

Resonant optical excitation dramatically renormalizes the magnon spectrum.

Near-total collapse of the magnon gap observed.

Exchange interaction reduced by nearly 90% in the near-surface region.

Abstract

Femtosecond optical pulses have opened a new frontier in ultrafast dynamics, enabling direct access to fundamental interactions in quantum materials. In antiferromagnets (AFMs), where the fundamental quantum mechanical exchange interaction governs spin dynamics, this access is especially compelling, enabling the excitation of magnons - collective spin-wave modes - that naturally reach terahertz (THz) frequencies and supersonic velocities. Femtosecond optical pulses provided a route to coherently excite such magnons across the entire Brillouin zone. Controlling their spectral properties - such as the magnon gap and dispersion - represents the next monumental step, enabling dynamic tuning of group velocities, coherence, and interaction pathways. Yet, achieving this remains a challenge, requiring ultrafast and long-lasting manipulation of the underlying exchange interaction. Here, we show that in DyFeO3 - an insulating AFM with strongly coupled electronic and magnetic degrees of freedom - resonant above-bandgap optical excitation leads to a dramatic renormalization of the THz magnon spectrum, including a near-total collapse of the magnon gap. Our analysis reveals this transformation to be consistent with a transient reduction of the exchange interaction by nearly 90% in the near-surface nanoscale region. These findings establish a pathway for light-driven, nanoscale control of AFM spin dynamics, opening opportunities for reconfigurable, high-speed magnonic and spintronic applications.