Demonstration of ultrafast coherent sub-picosecond magnon pulses

Peter Kubaščík; Miina Leiviskä; Martin Bušina; Zdenek Kašpar; Katharina Müller; Jonathan Mak; Monika Scheufele; Gal Lemut; Jose Solano; Oliver Franke; Rostislav Matuška; Jiří Jechumtál; Eva Schmorranzerová; Petr Němec; Petr Kužel; Tobias Kampfrath; Piet W. Brouwer; Matthias Opel; Stephan Geprägs; Matthias Althammer; Tomáš Jungwirth; Helena Reichlova; Lukáš Nádvorník

arXiv · 2610.11550

Demonstration of ultrafast coherent sub-picosecond magnon pulses

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Abstract

Ultrafast magnonics explores routes towards energy-efficient information processing by replacing electrons with pulses of terahertz magnons. The critical, but so far elusive, requirement on the magnon pulses is the combination of high-speed and a long-range propagation while maintaining a well-defined narrow waveform of the pulses. Here, we demonstrate the launching of 0.4-picosecond magnon pulses in the altermagnetic insulator $α$-Fe$_2$O$_3$ (hematite) using broadband terahertz spin-orbit torques by an adjacent platinum layer. Phase-resolved terahertz transmission reveals that these sub-picosecond pulses travel ballistically, coherently and non-dispersively at a constant velocity of 23 nm/ps, transport angular momentum and retain their temporal waveform shape over 160 nm, with an inferred relaxation length in hundreds of nanometers or more. Beyond establishing $α$-Fe$_2$O$_3$ as an optimal platform for ultrafast magnonics, our technique introduces a high-resolution, tabletop method to directly extract dispersion relations up to high wavevectors, and explore ultrafast magnon dynamics in altermagnets and other magnetic materials with teraherz-range dynamics.

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Peter Kubaščík, Miina Leiviskä, Martin Bušina, Zdenek Kašpar, Katharina Müller, Jonathan Mak, Monika Scheufele, Gal Lemut, Jose Solano, Oliver Franke, Rostislav Matuška, Jiří Jechumtál, Eva Schmorranzerová, Petr Němec, Petr Kužel, Tobias Kampfrath, Piet W. Brouwer, Matthias Opel, Stephan Geprägs, Matthias Althammer, Tomáš Jungwirth, Helena Reichlova, Lukáš Nádvorník. 2026-10-08. Demonstration of ultrafast coherent sub-picosecond magnon pulses. https://arxiv.org/abs/2610.11550

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