Charged skyrmions on the surface of a topological insulator

Hurst, Hilary M.; Efimkin, Dmitry K.; Zang, Jiadong; Galitski, Victor

doi:10.1103/physrevb.91.060401

Cited by 45 publications

(57 citation statements)

References 45 publications

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“…We thus employ the "hard-wall" approximation n z (ρ) = sgn(ρ−R S ), with R S the skyrmion radius 29 . Such a structure is likely to be realized under a strong out-of-plane magnetic anisotropy.…”

Section: Single-skyrmion Problemmentioning

confidence: 99%

“…Since the exchange coupling between the local in-plane magnetization and the TI surface electron can be regarded as the emergent gauge field (vector potential) for the conduction electrons 25 , topological magnetic textures on TI surfaces can give rise to even richer electronic properties: vortices and domain walls, for instance, are supposed to host zero modes, leading to electric charging of those textures [26][27][28] . Recent theoretical studies predict that magnetic skyrmions on TI surface can be charged as well 29,30 . Transport measurements in magnetic TI heterostructures discovered the coexistence of the THE related to the real-space Berry curvature from skyrmions and the AHE related to momentum-space counterpart from SOC 31 , while the transport is dominated by the bulk states, leaving the surface transport ambiguous.…”

Section: Introductionmentioning

confidence: 99%

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Skyrmion-induced anomalous Hall conductivity on topological insulator surfaces

Araki¹,

Nomura

2017

Phys. Rev. B

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Electron spin-momentum locking together with background magnetic textures can significantly alter the electron transport properties. We theoretically investigate the electron transport at the interface between a topological insulator and a magnetic insulator with magnetic skyrmions on the top. In contrast to the conventional topological Hall effect in normal metals, the skyrmions yield an additional contribution to the anomalous Hall conductivity even in the absence of in-plane magnetic texture, arising from the phase factor characteristic to Dirac electrons acquired at skyrmion boundary.

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Section: Single-skyrmion Problemmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Skyrmion-induced anomalous Hall conductivity on topological insulator surfaces

Araki¹,

Nomura

2017

Phys. Rev. B

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“…In the short wavelength regime, the resonant states manifested as confined vortices inside of the skyrmion structure can be exploited for electrically charging the skyrmion structure [32,33], enabling the surface electrons on the TI to drive skyrmion motion with a low current and high thermal efficiency. In the long wavelength regime, the strong and robust directionality for skew scattering may be exploited for device application based on the anomalous Hall effect.…”

Section: Discussionmentioning

confidence: 99%

“…For a swirling skyrmion structure, the emergent magnetic field B is zero and the in-plane component can be gauged away [33,34]. In this case, the "hard-wall" approximation n z (r) = ±1 can be invoked [33,34], with the point inside and outside of the skyrmion structure taking on the value of minus one and one (n 1 = 1, n 2 = −1), respectively. In experiments, such a structure can be realized using materials with a strong out-of-plane magnetic anisotropy.…”

Section: Model and Methodsmentioning

confidence: 99%

“…Efforts in improving thermal efficiency and better manipulating skyrmions have led to the "marriage" between skyrmion and TI, where skyrmions arise on the surface of a TI. Electric charging of magnetic vortices on the surface of a TI was investigated [32], and the confinement state in the skyrmion structure on the surface of a TI was discovered, paving the way to driving skyrmion motion using an applied electric field [33]. Electron skew scattering induced by the skyrmion structure on the TI surface was also studied [34].…”

Section: Introductionmentioning

confidence: 99%

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Scattering of Dirac electrons from a skyrmion: Emergence of robust skew scattering

Wang

Lai

2020

Phys. Rev. Research

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We study electron scattering from a closed magnetic structure embedded in the top surface of a topological insulator (TI). Outside of the structure there is a uniform layer of ferromagnetic insulator (FMI), leading to a positive effective mass for the Dirac electrons. The mass inside the structure can be engineered to be negative, leading to a skyrmion structure. The geometric shape of the structure can be circular or deformed, leading to integrable or chaotic dynamics, respectively, in the classical limit. For a circular structure, the relativistic quantum scattering characteristics can be calculated analytically. For a deformed structure, we develop an efficient numerical method, the multiple multipole method, to solve the scattering wavefunctions. We find that, for scattering from a skyrmion, anomalous Hall effect as characterized by strong skew scattering can arise, which is robust against structural deformation due to the emergence of resonant modes. In the short (long) wavelength regime, the resonant modes manifest themselves as confined vortices (excited edge states). The origin of the resonant states is the spin phase factor of massive Dirac electrons at the skyrmion boundary. Further, in the short wavelength regime, for a circular skyrmion, a large number of angular momentum channels contribute to the resonant modes. In this regime, in principle, classical dynamics are relevant, but we find that geometric deformations, even those as severe as leading to fully developed chaos, have little effect on the resonant modes. The vortex structure of the resonant states makes it possible to electrically "charge" the skyrmion, rendering feasible to manipulate its motion electrically. In the long wavelength regime, only the lowest angular momentum channels contribute to the resonant modes, making the skew scattering sharply directional. These phenomena can be exploited for applications in generating dynamic skyrmions for information storage and in Hall devices.

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Ferrimagnetic Skyrmions in Topological Insulator/Ferrimagnet Heterostructures

Groß

Dai

et al. 2020

Advanced Materials

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Magnetic skyrmions are topologically nontrivial chiral spin textures that have potential applications in next‐generation energy‐efficient and high‐density spintronic devices. In general, the chiral spins of skyrmions are stabilized by the noncollinear Dzyaloshinskii–Moriya interaction (DMI), originating from the inversion symmetry breaking combined with the strong spin–orbit coupling (SOC). Here, the strong SOC from topological insulators (TIs) is utilized to provide a large interfacial DMI in TI/ferrimagnet heterostructures at room temperature, resulting in small‐size (radius ≈ 100 nm) skyrmions in the adjacent ferrimagnet. Antiferromagnetically coupled skyrmion sublattices are observed in the ferrimagnet by element‐resolved scanning transmission X‐ray microscopy, showing the potential of a vanishing skyrmion Hall effect and ultrafast skyrmion dynamics. The line‐scan spin profile of the single skyrmion shows a Néel‐type domain wall structure and a 120 nm size of the 180° domain wall. This work demonstrates the sizable DMI and small skyrmions in TI‐based heterostructures with great promise for low‐energy spintronic devices.

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Charged skyrmions on the surface of a topological insulator

Cited by 45 publications

References 45 publications

Skyrmion-induced anomalous Hall conductivity on topological insulator surfaces

Skyrmion-induced anomalous Hall conductivity on topological insulator surfaces

Scattering of Dirac electrons from a skyrmion: Emergence of robust skew scattering

Ferrimagnetic Skyrmions in Topological Insulator/Ferrimagnet Heterostructures

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