research highlights

ACTIVE MATTER own accord. The skyrmions interacted BIOMECHANICS Skyrmion school elastically with their neighbours, which led Fall forward Nat. Commun. 10, 4744 (2019) to collective effects — such as re-assembly or J. R. Soc. Interface 16, 20190292 (2019) formation of chains and clusters. ED Consider for a moment how something as https://doi.org/10.1038/s41567-019-0716-0 innate to us as running or jumping actually works. The complexity of such seemingly simple tasks still keeps those who engineer robots or wearable devices busy. Taylor Dick UNCONVENTIONAL SUPERCONDUCTIVITY and co-workers have now investigated the Triplet no more mechanics of our capacity to stand upright Nature 574, 72–75 (2019) when encountering changing terrain or — put more simply — when falling into a hole. For two decades, strontium ruthenate The team had people hop on a platform has been the leading candidate for a and used motion capture to record the solid-state realization of chiral p-wave coordinated kinetics and kinematics of superconductivity. This is important their lower-limb joints when the platform because this form of superconductivity has was suddenly pulled from under their feet. an unusual triplet order parameter and is Calculations of the mechanical work and Credit: under a Creative Commons licence predicted to host Majorana fermions. Now, power at each joint showed that we are able (http://creativecommons.org/licenses/by/4.0/) Andrej Pustogow and co-workers have to recover from short falls — up to 10 cm — ruled out this interpretation by conducting with minimal changes to our legs’ mechanics careful nuclear magnetic resonance as the ankles absorb the shock. Fall higher, Schools of fish can move in an organized experiments. however, and the hopping mechanics change manner because each fish tries to match its This technique is sensitive to the to redistribute the shock to the higher joints movements to its neighbours. As fish don’t symmetry of the order parameter via the — knees and hips — possibly to prevent necessarily lend themselves to controlled change in the Knight shift upon entering damage to our smaller distal muscles. FL parameter studies, it is fortunate that the the superconducting state. The authors https://doi.org/10.1038/s41567-019-0717-z same collective effects that make a school of found a substantial reduction at the critical fish swim as one can also arise in synthetic temperature, indicative of a decrease in the TOPOLOGICAL PHOTONICS systems. These make attractive experimental magnetization and therefore an absence of test beds of schooling dynamics — especially the spin polarization that would be expected Reconfgurable routing if they use readily available technology. for a triplet state. This demonstrates that the Science 365, 1163–1166 (2019) Hayley Sohn and colleagues have now shown superconductivity in strontium ruthenate is A signal sent across a chip doesn’t arrive that skyrmions in liquid crystals can display likely of singlet character. at its full strength because of losses. On collective effects similar to a school of fish. There are still many exotic options for optical chips these come mainly from In their experiments, the skyrmions — what exactly that state might be. These results defects, but the scattering-free optical modes stable topological structures — were formed mark a new stage in our understanding propagating along an interface between two in the director field of the liquid crystal. An of both triplet superconductivity and topologically different regions may solve this oscillating electric field applied to the crystal strontium ruthenate. DA problem. Photonic topological properties are cell broke the symmetry of the system and defined by the physical structure, making allowed the skyrmions to move of their https://doi.org/10.1038/s41567-019-0715-1 such waveguides rigid — like traces on a circuit board. Han Zhao and colleagues were able to steer topological modes along NUCLEAR PHYSICS optically reconfigurable paths. The team exploited the interplay of Of all shapes Phys. Rev. Lett. 123, 142502 (2019) topological and non-Hermitian symmetries, where new topological states emerge for a Nuclei come in various shapes — from spheres to deformed ellipsoids, which can coexist, specific contrast between gain and loss in the so that a nucleus with a spherical ground state may possess a deformed excited state, system. By optically pumping some regions of or vice versa. Shape coexistence is mostly observed for nuclei with proton or neutron a microring lattice patterned onto an InGaAsP- numbers that almost fill up a nuclear shell, such as in cadmium-110 with 48 protons. based multiple quantum well, they generated Now, Paul Garrett and colleagues have reported spectroscopic studies of the an overlay structure of optical gain and intrinsic structure of the stable cadmium-110 and cadmium-112 isotopes combined with beyond- material loss in such a way that a topological mean-field calculations. The results suggested that at least three different shapes mode was created on the boundary between coexist in these nuclei. In contrast to the prevalent view that low-energy excitations the two regions, whose shape can be flexibly in cadmium nuclei are caused by vibrations around a spherical nucleus, the authors controlled by patterning the illumination. NM found that these excitations are deformed states, which do not possess vibrational wave functions. If confirmed, this result would challenge our understanding of nuclear https://doi.org/10.1038/s41567-019-0718-y structure because deformation might already appear at closed shells. SR David Abergel, Elizaveta Dubrovina, https://doi.org/10.1038/s41567-019-0719-x Federico Levi, Nina Meinzer and Stefanie Reichert

Nature Physics | VOL 15 | NOVEMBER 2019 | 1105 | www.nature.com/naturephysics 1105