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Condensed Matter > Mesoscale and Nanoscale Physics
Title: Archimedean Screw in Driven Chiral Magnets
(Submitted on 21 Dec 2020 (v1), last revised 27 May 2021 (this version, v4))
Abstract: In chiral magnets a magnetic helix forms where the magnetization winds around a propagation vector $\mathbf{q}$. We show theoretically that a magnetic field $\mathbf{B}_{\perp}(t) \perp \mathbf{q}$, which is spatially homogeneous but oscillating in time, induces a net rotation of the texture around $\mathbf{q}$. This rotation is reminiscent of the motion of an Archimedean screw and is equivalent to a translation with velocity $v_{\text{screw}}$ parallel to $\mathbf{q}$. Due to the coupling to a Goldstone mode, this non-linear effect arises for arbitrarily weak $\mathbf{B}_{\perp}(t) $ with $v_{\text{screw}} \propto |\mathbf{B}_{\perp}|^2$ as long as pinning by disorder is absent. The effect is resonantly enhanced when internal modes of the helix are excited and the sign of $v_{\text{screw}}$ can be controlled either by changing the frequency or the polarization of $\mathbf{B}_{\perp}(t)$. The Archimedean screw can be used to transport spin and charge and thus the screwing motion is predicted to induce a voltage parallel to $\mathbf{q}$. Using a combination of numerics and Floquet spin wave theory, we show that the helix becomes unstable upon increasing $\mathbf{B}_{\perp}$ forming a `time quasicrystal' which oscillates in space and time for moderately strong drive.
Submission history
From: Nina del Ser [view email][v1] Mon, 21 Dec 2020 18:29:29 GMT (22599kb,D)
[v2] Tue, 12 Jan 2021 13:18:36 GMT (40091kb,AD)
[v3] Tue, 23 Mar 2021 11:38:30 GMT (40082kb,AD)
[v4] Thu, 27 May 2021 20:35:42 GMT (40086kb,AD)
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