2020/12/31 by Nina del Ser, Lukas Heinen, Achim Rosch
Biochemistry, Genetics and Molecular Biology · Computer Science · Physics and Astronomy · #Algorithm #Artificial intelligence #Cellular Automata and Applications #Computational Physics and Python Applications #Computer science #Condensed matter physics #Coupling (piping) #Geomagnetism and Paleomagnetism Studies #Magnetic properties of thin films #Mathematical physics #Physics #cond-mat.mes-hall #cond-mat.str-el
paper · pdf · doi:10.21468/scipostphys.11.1.009
published in SciPost Physics 11(1) (SciPost.org) · 12 pages, 9 figures. Supplementary: 7 pages, 1 figure. V2: added references, added videos showing dynamics of driven system. V3: corrected mistake in Sec. VI: transport, and eq. F7 in App.F. In the limit $v_Fτ\ll q^{-1}$ current grows as $τ^2$, rather than being independent of $τ$ as previously claimed. Changes in v4: minor revisions following referee recommendations; typos corrected
arxiv created 2021/05/27 · openalex publication_date 2021/07/13 · arxiv updated 2021/11/10 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
In chiral magnets a magnetic helix forms where the magnetization winds around a propagation vector q <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mi>q</mml:mi> </mml:math> . We show theoretically that a magnetic field B_\bot(t) \bot q <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:msub> <mml:mi>B</mml:mi> <mml:mi>⊥</mml:mi> </mml:msub> <mml:mo stretchy="false" form="prefix">(</mml:mo> <mml:mi>t</mml:mi> <mml:mo stretchy="false" form="postfix">)</mml:mo> <mml:mi>⊥</mml:mi> <mml:mi>q</mml:mi> </mml:mrow> </mml:math> , which is spatially homogeneous but oscillating in time, induces a net rotation of the texture around q <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mi>q</mml:mi> </mml:math> . This rotation is reminiscent of the motion of an Archimedean screw and is equivalent to a translation with velocity vscrew <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msub> <mml:mi>v</mml:mi> <mml:mtext mathvariant="normal">screw</mml:mtext> </mml:msub> </mml:math> parallel to q. Due to the coupling to a Goldstone mode, this non-linear effect arises for arbitrarily weak B_\bot(t) <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:msub> <mml:mi>B</mml:mi> <mml:mi>⊥</mml:mi> </mml:msub> <mml:mo stretchy="false" form="prefix">(</mml:mo> <mml:mi>t</mml:mi> <mml:mo stretchy="false" form="postfix">)</mml:mo> </mml:mrow> </mml:math> with vscrew ∝ | B_⊥|2 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:msub> <mml:mi>v</mml:mi> <mml:mtext mathvariant="normal">screw</mml:mtext> </mml:msub> <mml:mo>∝</mml:mo> <mml:mo stretchy="false" form="prefix">|</mml:mo> <mml:msub> <mml:mi>B</mml:mi> <mml:mo>⊥</mml:mo> </mml:msub> <mml:msup> <mml:mo stretchy="false" form="prefix">|</mml:mo> <mml:mn>2</mml:mn> </mml:msup> </mml:mrow> </mml:math> 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 vscrew <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msub> <mml:mi>v</mml:mi> <mml:mtext mathvariant="normal">screw</mml:mtext> </mml:msub> </mml:math> can be controlled either by changing the frequency or the polarization of B_\bot(t) <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:msub> <mml:mi>B</mml:mi> <mml:mi>⊥</mml:mi> </mml:msub> <mml:mo stretchy="false" form="prefix">(</mml:mo> <mml:mi>t</mml:mi> <mml:mo stretchy="false" form="postfix">)</mml:mo> </mml:mrow> </mml:math> . 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, we show that the helix becomes unstable upon increasing B_\bot <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msub> <mml:mi>B</mml:mi> <mml:mi>⊥</mml:mi> </mml:msub> </mml:math> , forming a `time quasicrystal’ which oscillates in space and time for moderately strong drive.