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Register a new userInteraction of a Neel-type skyrmion and a superconducting vortex
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Superconductor-ferromagnet heterostructures hosting vortices and skyrmions are new area of an interplay between superconductivity and magnetism. We study an interaction of a Neel-type skyrmion and a Pearl vortex in thin heterostructures due to stray fields. Surprisingly, we find that it can be energetically favorable for the Pearl vortex to be situated at some nonzero distance from the center of the Neel-type skyrmion. The presence of a vortex-antivortex pair is found to result in increase of the skyrmion radius. Our theory predicts that a spontaneous generation of a vortex-anti-vortex pair is possible under some conditions in the presence of a Neel-type skyrmion.
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We consider a type-II superconducting thin film in contact with a Neel skyrmion. The skyrmion induces spontaneous currents in the superconducting layer, which under the right condition generate a superconducting vortex in the absence of an external magnetic field. We compute the magnetic field and current distributions in the superconducting layer in the presence of Neel skyrmion.
Interactions between vortices in thin superconducting films are investigated in the crossover (intertype) regime between superconductivity types I and II. We consider two main factors responsible for this crossover: a) changes in the material characteristics of the film and b) variations of the film thickness controlling the effect of the stray magnetic fields outside superconducting sample. The analysis is done within the formalism that combines the perturbation expansion of the microscopic equations to one order beyond the Ginzburg-Landau theory with the leading contribution of the stray fields. It is shown that the latter gives rise to qualitatively different spatial profile and temperature dependence of the vortex interaction potential, as compared to bulk vortex interactions. The resulting interaction is long-range repulsive while exhibiting complex competition of attraction and repulsion at small and intermediate separations of vortices. This explains the appearance of vortex chains reported earlier for superconducting films.
We report experimental coupling of chiral magnetism and superconductivity in [IrFeCoPt]/Nb heterostructures. The stray field of skyrmions with radius ~50nm is sufficient to nucleate antivortices in a 25nm Nb film, with unique signatures in the magnetization, critical current and flux dynamics, corroborated via simulations. We also detect a thermally-tunable Rashba-Edelstein exchange coupling in the isolated skyrmion phase. This realization of a strongly interacting skyrmion-(anti)vortex system opens a path towards controllable topological hybrid materials, unattainable to date.
The current distribution across the thickness of a current-carrying rectangular film in the Meissner state was established long ago by the London brothers. The distribution across the width is more complicated but was later shown to be highly non-uniform, diverging at the edges. Accordingly, the standard view for type II superconductors is that vortices enter at the edges and, with increasing current, are driven inwards until they self-annihilate at the centre, causing dissipation. This condition is presumed to define the critical current. However we have shown that, under self-field (no external field), the transport critical current is a London surface current where the surface current density equals the critical field divided by {lambda}, across the entire width. The critical current distribution must therefore be uniform. Here we report studies of the current and field distribution across commercial YBa2Cu3O7 conductors and confirm the accepted non-uniform distribution at low current but demonstrate a radical crossover to a uniform distribution at critical current. This crossover ends discontinuously at a singularity and calculations quantitatively confirm these results in detail. The onset of self-field dissipation is, unexpectedly, thermodynamic in character and the implied vortex-free critical state seems to require new physics.
Vortices trapped in thin-film superconducting microwave resonators can have a significant influence on the resonator performance. Using a variable-linewidth geometry for a weakly coupled resonator we are able to observe the effects of a single vortex trapped in the resonator through field cooling. For resonant modes where the vortex is near a current antinode, the presence of even a single vortex leads to a measurable decrease in the quality factor and a dispersive shift of the resonant frequency. For modes with the vortex located at a current node, the presence of the vortex results in no detectable excess loss and, in fact, produces an increase in the quality factor. We attribute this enhancement to a reduction in the density of nonequilibrium quasiparticles in the resonator due to the suppressed gap from the vortex.
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