A photonic Weyl system by design: Theoretically proposed exotic physics is now being explored and realized in condensed matter and photonic systems. Weyl physics arises when the valence band and conduction bands meet at discrete points in the band structure. Jia et al. designed and fabricated a photonic metamaterial in which the position of the Weyl points in momentum space could be tuned using a huge artificial magnetic field. Because these points are stable, the ability to design and control such a Weyl system with a robust chiral optical mode could be exploited in future optical information processing applications. Science , this issue p. 148

Stretchable organic light-emitting devices are becoming increasingly important in the fast-growing fields of wearable displays, biomedical devices and health-monitoring technology. Although highly stretchable devices have been demonstrated, their luminous efficiency and mechanical stability remain impractical for the purposes of real-life applications. This is due to significant challenges arising from the high strain-induced limitations on the structure design of the device, the materials used and the difficulty of controlling the stretch-release process. Here we have developed a laser-programmable buckling process to overcome these obstacles and realize a highly stretchable organic light-emitting diode with unprecedented efficiency and mechanical robustness. The strained device luminous efficiency −70 cd A⁻¹ under 70% strain - is the largest to date and the device can accommodate 100% strain while exhibiting only small fluctuations in performance over 15,000 stretch-release cycles. This work paves the way towards fully stretchable organic light-emitting diodes that can be used in wearable electronic devices.

An ultrathin, ultrasmooth and flexible Au film as an alternative of the indium–tin oxide (ITO) electrode in organic light-emitting devices (OLEDs) has been reported. The 7 nm Au film shows excellent surface morphology, optical and electronic characteristics including a root-mean-square roughness of 0.35 nm, a high transparency of 72% at 550 nm, and a sheet resistance of 23.75 Ω sq⁻¹. These features arise from the surface modification of the glass substrate by using a SU-8 film, which fixes metal atoms via chemical bond interactions between Au and SU-8 film to suppress the island growth mode. A 17% enhancement in current efficiency has been obtained from the OLEDs based on the ultrathin Au electrodes compared to that of the devices with the ITO electrodes. The OLEDs with the ultrathin Au/SU-8 anodes exhibit high flexibility and mechanical robustness.

Topology in higher dimensions: In condensed-matter systems, the band structure of a material has often been equated with functionality. However, consideration of the topology of the band structure now provides a route to develop a functionality that goes far beyond the expected properties of the materials. Using electromagnetic metamaterials as building blocks, Ma et al . realized a five-dimensional generalization of a topological Weyl semimetal. Along with the three real momentum dimensions, these included two bi-anisotropy material parameters as synthetic dimensions to demonstrate both linked Weyl surfaces and Yang monopoles. The metamaterial platform provides a powerful route to explore the exotic physics associated with higher-order topological phenomena. —ISO