Jilei Chen's group at the Shenzhen International Quantum Academy (IQASZ), Shenzhen, in collaboration with the groups of Prof. Pietro Gambardella at ETH Zurich, Switzerland, Prof. Rembert A. Duine at Utrecht University, the Netherlands, and Prof. Haiming Yu at Beihang University, has reported advances in spin-orbit-torque-driven antimagnons. Using Brillouin light scattering spectroscopy in Pt/BiYIG thin-film devices, the team directly observed, for the first time, the inverted dispersion and left-handed precession of antimagnons. These findings establish a new experimental platform for investigating nonequilibrium amagnonic phenomena. The study was published in Physical Review Letters on September 16, 2026, under the title "Direct Observation of Antimagnons with Inverted Dispersion."

Figure 1. Schematic illustration of antimagnon detection.

Antimagnons are negative-energy excitations of a dynamically stabilized inverted magnetization state. In contrast to conventional magnons, antimagnons are theoretically predicted to exhibit a frequency that decreases with increasing wave-vector magnitude, resulting in an inverted dispersion. Direct spectroscopic evidence of this behavior had, however, remained elusive. To address this challenge, the team fabricated high-quality bismuth-substituted yttrium iron garnet (BiYIG) films and used strain engineering to tune their perpendicular magnetic anisotropy to nearly compensate the demagnetizing field. Spin-orbit torque (SOT) was then employed to drive the system, enabling auto-oscillations at low current densities in devices with lateral dimensions on the order of 100 micrometers, as well as experimental observation of the antimagnon dispersion relation.

Figure 2. Brillouin light scattering spectra and corresponding dispersion relations in the thermal-magnon, auto-oscillation, and antimagnon regimes.

Wave-vector-resolved Brillouin light scattering (BLS) spectroscopy was used to systematically investigate the evolution of magnon dynamics with current density. As the current density increased, the system passed through three distinct regimes: thermal magnons at low currents, auto-oscillations above the first current threshold, and an antimagnon state above a second threshold. The transition to the antimagnon state was accompanied by an abrupt decrease in resonance frequency from approximately 2.2 to 1.7 GHz. Near the critical point, two spectral peaks associated with conventional magnons and antimagnons appeared simultaneously, indicating their coexistence. BLS measurements further revealed that antimagnons exhibit left-handed precession and carry spin angular momentum opposite to that of conventional magnons. Micromagnetic simulations reproduced the dispersion characteristics of all three regimes and the coexistence of magnons and antimagnons near the threshold. By providing the first direct experimental evidence of inverted dispersion and left-handed precession in antimagnons, this work extends the conventional understanding of magnon dispersion. It connects chiral spin dynamics, SOT, and magnon transport, and may facilitate the development of low-power, high-performance magnonic information-processing devices based on antimagnons.

The first authors of the study are Hanchen Wang, a doctoral student at ETH Zurich and a former visiting student at IQASZ; Junfeng Hu and Wenjie Song, assistant research fellows at IQASZ; and Artim L. Bassant, a doctoral student at Utrecht University. The corresponding authors are Hanchen Wang; Prof. Rembert A. Duine of Utrecht University; Prof. Pietro Gambardella of ETH Zurich; and Prof. Haiming Yu of Beihang University. This work was supported by the National Key Research and Development Program of China, the National Natural Science Foundation of China, the the Shenzhen Science and Technology Program, and other funding.

Paper Link：https://doi.org/10.1103/2g7f-5dlb