Achim Rosch
In chiral magnets a helical magnetic texture forms where the magnetization winds around a propagation vector q. We show theoretically [1] that a magnetic field which is spatially homogeneous but oscillating in time, induces a net rotation of the texture around q. This rotation is reminiscent of the motion of an Archimedean screw and is equivalent to a translation with finite velocity. Technically, it arises due to the coupling of the oscillations to an overdamped Goldstone mode. The Archimedean screw can be used to transport spin and charge and thus the screwing motion is predicted to induce a voltage parallel to q. Using a combination of numerics and Floquet spin wave theory in a dissipative system, we show that the helix becomes unstable upon increasing the oscillating field forming a `time quasicrystal', oscillating in space and time for moderately strong drive.
[1] Nina del Ser, Lukas Heinen, Achim Rosch, arXiv:2012.11548