Skyrmions all round

Abstract

NATURE PHYSICS | VOL 11 | NOVEMBER 2015 | www.nature.com/naturephysics 891 research highlights FERROELECTRICS Skyrmions all round Nature Commun. 6, 8542 (2015) The swirling spin textures known as skyrmions have generated great interest in the magnetics community. Stabilized by chiral interactions, these vortex-like excitations are topologically non-trivial, making them fairly robust against perturbations and useful for a range of technological applications. As ferroelectric compounds lack chiral interactions, one might expect that such textures cannot form in these materials, but this may not be the case. Using first-principles-based methods, Yousra Nahas and colleagues have shown that a combination of geometric confinement and dipolar interactions can stabilize a skyrmionic configuration of polarization in ferroelectric nanocomposites. Although, at first glance, they seem similar to magnetic skyrmions, electrical skyrmions have a distinct topological charge density that has four-fold, rather than cylindrical symmetry. Perhaps more interestingly, they can be stabilized down to just a few nanometres, which will surely interest those working to develop skyrmion-based devices. Unfortunately, such polarization textures do not seem to be stable at anywhere near room temperature. But the same was said of their magnetic counterparts, which recently achieved this feat. So although experimental confirmation is yet to materialize, one wonders how far extrinsic topological protection can be pushed in ferroelectrics. LF ASTROPHYSICS Useful glitches Science Adv. 1, e1500578 (2015) Much like young people, young pulsars don't like to play by the rules. Their very fast rotation period, which is extremely stable for older pulsars, exhibits abrupt changes known as glitches. During these glitches the pulsar suddenly starts to spin faster for a short period of time. This is believed to be the result of the interactions between the normal matter in the outer crust of the star and the superfluid inner crust. But the estimated superfluid reservoir needed to explain the observational data is larger than that available in the crust. To explain this, Wynn Ho and colleagues have suggested that the superfluid extends to the core of the star. Ho et al. tested several superfluid models, providing the additional moment of inertia needed to explain the pulsar glitches. One such model successfully accounted for the observational data and the temperature dependence of superfluidity. And this turns out to have an unexpected application: using the pulsar glitch data and the interior temperature, one can determine the mass of the star. IG ROSETTA MISSION