Thermally driven ratchet motion of a skyrmion microcrystal and topological magnon Hall effect
Remarkably stable excitations known as skyrmions have recently garnered significant attention in condensed-matter systems. It is now shown that skyrmions in thin films of MnSi and Cu 2 OSeO 3 can be made to rotate as a result of thermal fluctuations. Spontaneously emergent chirality is an issue of f...
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Veröffentlicht in: | Nature materials 2014-03, Vol.13 (3), p.241-246 |
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Zusammenfassung: | Remarkably stable excitations known as skyrmions have recently garnered significant attention in condensed-matter systems. It is now shown that skyrmions in thin films of MnSi and Cu
2
OSeO
3
can be made to rotate as a result of thermal fluctuations.
Spontaneously emergent chirality is an issue of fundamental importance across the natural sciences
1
. It has been argued that a unidirectional (chiral) rotation of a mechanical ratchet is forbidden in thermal equilibrium, but becomes possible in systems out of equilibrium
2
. Here we report our finding that a topologically nontrivial spin texture known as a skyrmion—a particle-like object in which spins point in all directions to wrap a sphere
3
—constitutes such a ratchet. By means of Lorentz transmission electron microscopy we show that micrometre-sized crystals of skyrmions in thin films of Cu
2
OSeO
3
and MnSi exhibit a unidirectional rotation motion. Our numerical simulations based on a stochastic Landau–Lifshitz–Gilbert equation suggest that this rotation is driven solely by thermal fluctuations in the presence of a temperature gradient, whereas in thermal equilibrium it is forbidden by the Bohr–van Leeuwen theorem
4
,
5
. We show that the rotational flow of magnons driven by the effective magnetic field of skyrmions gives rise to the skyrmion rotation, therefore suggesting that magnons can be used to control the motion of these spin textures. |
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ISSN: | 1476-1122 1476-4660 |
DOI: | 10.1038/nmat3862 |