Topological Magnons and Edge States in Antiferromagnetic Skyrmion Crystals

Recent advances in the physics of current-driven antiferromagnetic skyrmions have observed the absence of a Magnus force. We outline the symmetry reasons for this phenomenon, and show that this cancellation will fail in the case of spin polarized currents. Pairing micromagnetic simulations with semiclassical spin wave transport theory, we demonstrate that skyrmions produce a spin-polarized transverse magnon current, and that spin-polarized magnon currents can in turn produce transverse motion of antiferromagnetic skyrmions. We examine qualitative differences in the frequency dependence of the skyrmion Hall angle between ferromagnetic and antiferromagnetic cases, and close by proposing a simple skyrmion-based magnonic device for demultiplexing of spin channels.arXiv:1902.09382v2 [cond-mat.mes-hall]

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“…A more quantiative analysis of this result has recently been developed from lattice-level transport theory. 49…”

Section: Skyrmion-induced Magnon Hall Effectmentioning

confidence: 99%

Topological spin Hall effects and tunable skyrmion Hall effects in uniaxial antiferromagnetic insulators

Daniels

Cheng

et al. 2019

Phys. Rev. B

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“…Realizing such control could be attained in topological magnon insulators [16][17][18], systems with a spatially periodic magnetic texture that support topologically protected magnonic edge states. A promising platform for the nascent field of topological magnonics [19][20][21] are ferromagnetic skyrmion crystals (FM-SkXs) [22,23], whose magnetic texure is shown in Fig. 1.…”

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confidence: 99%

Chiral magnonic edge states in ferromagnetic skyrmion crystals controlled by magnetic fields

Díaz

Hirosawa

Klinovaja

et al. 2020

Phys. Rev. Research

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Achieving control over magnon spin currents in insulating magnets-where dissipation due to Joule heating is highly suppressed-is an active area of research that could lead to energy-efficient spintronics applications. However, magnon spin currents supported by conventional systems with uniform magnetic order have proven hard to control. An alternative approach that relies on topologically protected magnonic edge states of spatially periodic magnetic textures has recently emerged. A prime example of such textures is the ferromagnetic skyrmion crystal which hosts chiral edge states providing a platform for magnon spin currents. Here, we show, for the first time, an external magnetic field can drive a topological phase transition in the spin wave spectrum of a ferromagnetic skyrmion crystal. The topological phase transition is signaled by the closing of a low-energy bulk magnon gap at a critical field. In the topological phase, below the critical field, two topologically protected chiral magnonic edge states lie within this gap, but they unravel in the trivial phase, above the critical field. Remarkably, the topological phase transition involves an inversion of two magnon bands that at the Γ point correspond to the breathing and anticlockwise modes of the skyrmions in the crystal. Our findings suggest that an external magnetic field could be used as a knob to switch on and off magnon spin currents carried by topologically protected chiral magnonic edge states. arXiv:1910.05214v1 [cond-mat.str-el]

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“…Edge states have previously been proposed to occur in skyrmion systems, such as for frustrated magnets [65] where a dc current can induce motion on the edges of the sample; however, this effect is very different from the edge transport we propose here and it occurs due to a different mechanism. Chiral magnonic edge states for antiferromagnetic skyrmion crystals have also been proposed [66], but these differ from the edge current and skyrmion transport that we consider here. We note that our results do show similarities with recent studies of edge transport in chiral active matter or active spinning systems, where directed transport can occur near the edge of the sample or between regions of spinners of opposite chirality [7].…”

Section: Discussionmentioning

confidence: 63%

Chiral edge currents for ac-driven skyrmions in confined pinning geometries

Reichhardt

2019

Phys. Rev. B

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We show that ac driven skyrmion lattices in a weak pinning channel confined by regions of strong pinning exhibit edge transport carried by skipping orbits while skyrmions in the bulk of the channel undergo localized orbits with no net transport. The magnitude of the edge currents can be controlled by varying the amplitude and frequency of the ac drive or by changing the ratio of the Magnus force to the damping term. We identify a localized phase in which the orbits are small and edge transport is absent, an edge transport regime, and a fluctuating regime that appears when the ac drive is strong enough to dynamically disorder the skyrmion lattice. We also find that in some cases, multiple rows of skyrmions participate in the transport due to a drag effect from the skyrmionskyrmion interactions. The edge currents are robust for finite disorder and should be a general feature of skyrmions interacting with confined geometries or inhomogeneous disorder under an ac drive. We show that similar effects can occur for skyrmion lattices at interfaces or along domain boundaries for multiple coexisting skyrmion species. The edge current effect provides a new method to control skyrmion motion, and we discuss the connection of these results with recent studies on the emergence of edge currents in chiral active matter systems and gyroscopic metamaterials.

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Topological Magnons and Edge States in Antiferromagnetic Skyrmion Crystals

Cited by 150 publications

References 63 publications

Topological spin Hall effects and tunable skyrmion Hall effects in uniaxial antiferromagnetic insulators

Topological spin Hall effects and tunable skyrmion Hall effects in uniaxial antiferromagnetic insulators

Chiral magnonic edge states in ferromagnetic skyrmion crystals controlled by magnetic fields

Chiral edge currents for ac-driven skyrmions in confined pinning geometries

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