Direct Observation of Vortex Dynamics in Superconducting Films with Regular Arrays of Defects

Harada, Ken; Kamimura, O.; Kasai, H.; Matsuda, Tsuyoshi; Tonomura, Akira; Moshchalkov, Victor

doi:10.1126/science.274.5290.1167

Cited by 580 publications

(437 citation statements)

References 18 publications

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“…There are other examples of particles moving over ordered substrates, such as vortices in type-II superconductors with periodic pinning arrays [41][42][43] or colloids placed on optically created periodic substrates 44,58 . In these systems the dynamics is overdamped; however, there can be directional locking effects in which the particles preferentially move along symmetry directions of the underlying substrate as the direction of drive is rotated with respect to the substrate lattice [45][46][47][48][49][50][51][52] .…”

Section: Introductionmentioning

confidence: 99%

Quantized transport for a skyrmion moving on a two-dimensional periodic substrate

2015

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We examine the dynamics of a skyrmion moving over a two-dimensional periodic substrate utilizing simulations of a particle-based skyrmion model. We specifically examine the role of the non-dissipative Magnus term on the driven motion and the resulting skyrmion velocity-force curves. In the overdamped limit, there is a depinning transition into a sliding state in which the skyrmion moves in the same direction as the external drive. When there is a finite Magnus component in the equation of motion, a skyrmion in the absence of a substrate moves at an angle with respect to the direction of the external driving force. When a periodic substrate is added, the direction of motion or Hall angle of the skyrmion is dependent on the amplitude of the external drive, only approaching the substrate-free limit for higher drives. Due to the underlying symmetry of the substrate the direction of skyrmion motion does not change continuously as a function of drive, but rather forms a series of discrete steps corresponding to integer or rational ratios of the velocity components perpendicular ( V ⊥ ) and parallel ( V || ) to the external drive direction: V ⊥ / V || = n/m, where n and m are integers. The skyrmion passes through a series of directional locking phases in which the motion is locked to certain symmetry directions of the substrate for fixed intervals of the drive amplitude. Within a given directionally locked phase, the Hall angle remains constant and the skyrmion moves in an orderly fashion through the sample. Signatures of the transitions into and out of these locked phases take the form of pronounced cusps in the skyrmion velocity versus force curves, as well as regions of negative differential mobility in which the net skyrmion velocity decreases with increasing external driving force. The number of steps in the transport curve increases when the relative strength of the Magnus term is increased. We also observe an overshoot phenomena in the directional locking, where the skyrmion motion can lock to a Hall angle greater than the clean limit value and then jump back to the lower value at higher drives. The skyrmion-substrate interactions can also produce a skyrmion acceleration effect in which, due to the non-dissipative dynamics, the skyrmion velocity exceeds the value expected to be produced by the external drive. We find that these effects are robust for different types of periodic substrates. Using a simple model for a skyrmion interacting with a single pinning site, we can capture the behavior of the change in the Hall angle with increasing external drive. When the skyrmion moves through the pinning site, its trajectory exhibits a side step phenomenon since the Magnus term induces a curvature in the skyrmion orbit. As the drive increases, this curvature is reduced and the side step effect is also reduced. Increasing the strength of the Magnus term reduces the range of impact parameters over which the skyrmion can be captured by a pinning site, which is one of the reasons that strong Magnus force effects reduce the...

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Section: Introductionmentioning

confidence: 99%

Quantized transport for a skyrmion moving on a two-dimensional periodic substrate

2015

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“…The ground state of the system is obtained by simulating field-cooled experiments [18]. We now consider a disk containing, e.g., 8 vortices in the field h = 15 (for R =1.5µm, this corresponds to H ≈ 45Oe).…”

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Pinning-Induced Formation of Vortex Clusters and Giant Vortices in Mesoscopic Superconducting Disks

et al. 2007

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Multi-quanta, or giant, vortices (GVs) are known to appear in very small superconductors near the superconducting transition due to strong confinement of magnetic flux. Here we present evidence for a new, pinning-related, mechanism for the formation of GVs. Using Bitter decoration to visualise vortices in small Nb disks, we show that confinement in combination with strong disorder causes individual vortices to merge into clusters or even GVs well below T c and H c2 , in contrast to well-defined shells of individual vortices found in the absence of pinning.Mesoscopic superconductors, i.e., such that they can accommodate only a small number of vortices, are known to exhibit complex and unique vortex structures due to the competition between surface superconductivity and vortex-vortex interactions [see e.g. 1-6]. For mesoscopic disks, theoretical studies found two kinds of superconducting states: a giant vortex (GV), i.e., a circular symmetric state with a fixed value of angular momentum that can carry several flux quanta [1,2] and multivortex states (MVS) with an effective total angular momentum corresponding to the number of vortices in the disk (vorticity L) [3]. Recently, it became possible to experimentally distinguish between a singlecore GV and a MVS composed of singly quantized vortices using the multiple-small-tunnel-junction

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“…It has been found that a periodic pinning landscape 1-11 leads to strong commensurability effects which appear when the number of vortices equals an integer (n) multiple of the number of pinning sites (i.e., at fields H = nH 0 with H 0 the first matching field where the number of vortices equals the number of pins), resulting in peaks in, e.g., the critical current as a function of applied magnetic field. However, at larger magnetic fields the pinning centers become repulsive potentials for the incoming vortices, resulting in excess vortices, located preferentially at the interstitial sites between the pinning centers, forming different type of ordered vortex configurations [12][13][14][15][16] . The interstitial vortices can be highly mobile and lead to strong reduction of the critical parameters of the system.…”

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confidence: 99%

Vortex interaction enhanced saturation number and caging effect in a superconducting film with a honeycomb array of nanoscale holes

et al. 2012

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Direct Observation of Vortex Dynamics in Superconducting Films with Regular Arrays of Defects

Cited by 580 publications

References 18 publications

Quantized transport for a skyrmion moving on a two-dimensional periodic substrate

Quantized transport for a skyrmion moving on a two-dimensional periodic substrate

Pinning-Induced Formation of Vortex Clusters and Giant Vortices in Mesoscopic Superconducting Disks

Vortex interaction enhanced saturation number and caging effect in a superconducting film with a honeycomb array of nanoscale holes

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