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Active matter, usually realized in biological systems, describes the collective properties of complex systems containing self-propelling units. Prominent examples include models of flocks of birds, swimming bacteria, or even the daily traffic jam.

Here, we pose the question of whether similar physics can be realized in condensed-matter systems driven out of equilibrium, for example, by external radiation. As an example, we study a ferrimagnet [1] in a weak oscillating magnetic field. In this model, domain walls are not static but move actively in a direction selected by spontaneous symmetry breaking. They thus act as self-propelling units. We show that this behavior arises from a phenomenon that we call dynamical frustration. Remarkably, even weakly driven systems can exhibit properties that are completely different from those of their equilibrium counterparts. Long-range correlations build up rapidly, and the system is highly resilient to noise. We also discuss how nonequilibrium phases can be realized in skyrmion systems [2].

 

[1] D. Hardt, R. Doostani, S. Diehl, N. del Ser, and A. Rosch, “Propelling ferrimagnetic domain walls by dynamical frustration,” Nature Comm. 16, 3817 (2025).

[2] F. Rucker, A. Bezvershenko, D. Mettus, A. Bauer, M. Garst, A. Rosch, and C. Pfleiderer, “Shaking and pushing skyrmions: Formation of a nonequilibrium phase with zero critical current,” Proc. of the Nat. Acad. of Sciences 123, e2507428123 (2026).

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